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 $115.59   9.291%   $126.3295   $126.33   $126.35   $126.30  
  Purchase #2 $168.68   5.132%   $177.3367   $177.34   $177.35   $177.30  
  Purchase #3 $42.82   11.165%   $47.6009   $47.60   $47.60   $47.60  
  Purchase #4 $137.41   4.446%   $143.5192   $143.52   $143.50   $143.50  
  Purchase #5 $96.49   6.480%   $102.7426   $102.74   $102.75   $102.70  
  Purchase #6 $146.28   4.297%   $152.5657   $152.57   $152.55   $152.60  
  Purchase #7 $165.87   11.515%   $184.9699   $184.97   $184.95   $185.00  
  7 purchase totals = $873.14       $935.0645   $935.07   $935.05   $935.00