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 $48.81   12.324%   $54.8253   $54.83   $54.85   $54.80  
  Purchase #2 $167.42   10.446%   $184.9087   $184.91   $184.90   $184.90  
  Purchase #3 $205.71   9.227%   $224.6909   $224.69   $224.70   $224.70  
  Purchase #4 $124.71   6.200%   $132.442   $132.44   $132.45   $132.40  
  Purchase #5 $125.71   9.149%   $137.2112   $137.21   $137.20   $137.20  
  Purchase #6 $29.84   5.210%   $31.3947   $31.39   $31.40   $31.40  
  Purchase #7 $11.58   9.645%   $12.6969   $12.70   $12.70   $12.70  
  7 purchase totals = $713.78       $778.1697   $778.17   $778.20   $778.10