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 $188.91   8.295%   $204.5801   $204.58   $204.60   $204.60  
  Purchase #2 $108.35   13.531%   $123.0108   $123.01   $123.00   $123.00  
  Purchase #3 $22.88   11.784%   $25.5762   $25.58   $25.60   $25.60  
  Purchase #4 $193.46   13.125%   $218.8516   $218.85   $218.85   $218.90  
  Purchase #5 $8.48   7.185%   $9.0893   $9.09   $9.10   $9.10  
  Purchase #6 $222.26   6.365%   $236.4068   $236.41   $236.40   $236.40  
  Purchase #7 $187.50   10.340%   $206.8875   $206.89   $206.90   $206.90  
  7 purchase totals = $931.84       $1,024.4023   $1,024.41   $1,024.45   $1,024.50