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 $240.95   8.288%   $260.9199   $260.92   $260.90   $260.90  
  Purchase #2 $185.90   8.237%   $201.2126   $201.21   $201.20   $201.20  
  Purchase #3 $159.87   10.257%   $176.2679   $176.27   $176.25   $176.30  
  Purchase #4 $79.84   9.290%   $87.2571   $87.26   $87.25   $87.30  
  Purchase #5 $181.78   3.338%   $187.8478   $187.85   $187.85   $187.80  
  Purchase #6 $152.36   12.659%   $171.6473   $171.65   $171.65   $171.60  
  Purchase #7 $61.42   13.810%   $69.9021   $69.90   $69.90   $69.90  
  7 purchase totals = $1,062.12       $1,155.0547   $1,155.06   $1,155.00   $1,155.00