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 $57.92   8.683%   $62.9492   $62.95   $62.95   $62.90  
  Purchase #2 $24.55   13.255%   $27.8041   $27.80   $27.80   $27.80  
  Purchase #3 $93.48   10.487%   $103.2832   $103.28   $103.30   $103.30  
  Purchase #4 $19.89   10.296%   $21.9379   $21.94   $21.95   $21.90  
  Purchase #5 $217.91   3.107%   $224.6805   $224.68   $224.70   $224.70  
  Purchase #6 $159.48   8.681%   $173.3245   $173.32   $173.30   $173.30  
  Purchase #7 $37.35   9.178%   $40.778   $40.78   $40.80   $40.80  
  7 purchase totals = $610.58       $654.7574   $654.75   $654.80   $654.70