Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.71   10.346%   $260.0966   $260.10   $260.10   $260.10  
  Purchase #2 $191.36   4.362%   $199.7071   $199.71   $199.70   $199.70  
  Purchase #3 $195.88   11.442%   $218.2926   $218.29   $218.30   $218.30  
  Purchase #4 $171.59   11.230%   $190.8596   $190.86   $190.85   $190.90  
  Purchase #5 $211.27   13.742%   $240.3027   $240.30   $240.30   $240.30  
  Purchase #6 $138.72   11.645%   $154.8739   $154.87   $154.85   $154.90  
  Purchase #7 $192.42   9.540%   $210.7769   $210.78   $210.80   $210.80  
  7 purchase totals = $1,336.95       $1,474.9094   $1,474.91   $1,474.90   $1,475.00