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 $76.78   12.560%   $86.4236   $86.42   $86.40   $86.40  
  Purchase #2 $59.28   4.514%   $61.9559   $61.96   $61.95   $62.00  
  Purchase #3 $178.76   8.555%   $194.0529   $194.05   $194.05   $194.10  
  Purchase #4 $22.79   8.527%   $24.7333   $24.73   $24.75   $24.70  
  Purchase #5 $152.63   3.478%   $157.9385   $157.94   $157.95   $157.90  
  Purchase #6 $127.42   10.430%   $140.7099   $140.71   $140.70   $140.70  
  Purchase #7 $83.75   5.634%   $88.4685   $88.47   $88.45   $88.50  
  7 purchase totals = $701.41       $754.2826   $754.28   $754.25   $754.30