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 $76.39   6.785%   $81.5731   $81.57   $81.55   $81.60  
  Purchase #2 $54.27   10.872%   $60.1702   $60.17   $60.15   $60.20  
  Purchase #3 $150.43   3.321%   $155.4258   $155.43   $155.45   $155.40  
  Purchase #4 $139.73   7.403%   $150.0742   $150.07   $150.05   $150.10  
  Purchase #5 $215.42   13.310%   $244.0924   $244.09   $244.10   $244.10  
  Purchase #6 $81.89   6.595%   $87.2906   $87.29   $87.30   $87.30  
  Purchase #7 $6.25   10.213%   $6.8883   $6.89   $6.90   $6.90  
  7 purchase totals = $724.38       $785.5146   $785.51   $785.50   $785.60