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 $58.49   12.766%   $65.9568   $65.96   $65.95   $66.00  
  Purchase #2 $57.46   8.679%   $62.447   $62.45   $62.45   $62.40  
  Purchase #3 $147.32   8.471%   $159.7995   $159.80   $159.80   $159.80  
  Purchase #4 $88.59   3.772%   $91.9316   $91.93   $91.95   $91.90  
  Purchase #5 $76.70   7.516%   $82.4648   $82.46   $82.45   $82.50  
  Purchase #6 $117.97   8.579%   $128.0906   $128.09   $128.10   $128.10  
  Purchase #7 $168.56   8.665%   $183.1657   $183.17   $183.15   $183.20  
  7 purchase totals = $715.09       $773.8560   $773.86   $773.85   $773.90