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 $35.34   9.108%   $38.5588   $38.56   $38.55   $38.60  
  Purchase #2 $165.95   4.381%   $173.2203   $173.22   $173.20   $173.20  
  Purchase #3 $46.95   3.647%   $48.6623   $48.66   $48.65   $48.70  
  Purchase #4 $30.47   6.154%   $32.3451   $32.35   $32.35   $32.30  
  Purchase #5 $206.42   8.841%   $224.6696   $224.67   $224.65   $224.70  
  Purchase #6 $170.39   7.684%   $183.4828   $183.48   $183.50   $183.50  
  Purchase #7 $31.31   3.238%   $32.3238   $32.32   $32.30   $32.30  
  7 purchase totals = $686.83       $733.2627   $733.26   $733.20   $733.30