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 $228.67   11.410%   $254.7612   $254.76   $254.75   $254.80  
  Purchase #2 $55.37   5.106%   $58.1972   $58.20   $58.20   $58.20  
  Purchase #3 $211.38   5.700%   $223.4287   $223.43   $223.45   $223.40  
  Purchase #4 $62.34   7.265%   $66.869   $66.87   $66.85   $66.90  
  Purchase #5 $142.66   10.429%   $157.538   $157.54   $157.55   $157.50  
  Purchase #6 $90.39   13.664%   $102.7409   $102.74   $102.75   $102.70  
  Purchase #7 $234.98   8.504%   $254.9627   $254.96   $254.95   $255.00  
  7 purchase totals = $1,025.79       $1,118.4977   $1,118.50   $1,118.50   $1,118.50