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 $119.93   11.377%   $133.5744   $133.57   $133.55   $133.60  
  Purchase #2 $123.66   10.409%   $136.5318   $136.53   $136.55   $136.50  
  Purchase #3 $146.65   5.661%   $154.9519   $154.95   $154.95   $155.00  
  Purchase #4 $245.73   8.556%   $266.7547   $266.75   $266.75   $266.80  
  Purchase #5 $100.74   4.589%   $105.363   $105.36   $105.35   $105.40  
  Purchase #6 $7.42   8.219%   $8.0298   $8.03   $8.05   $8.00  
  Purchase #7 $44.95   13.683%   $51.1005   $51.10   $51.10   $51.10  
  7 purchase totals = $789.08       $856.3061   $856.29   $856.30   $856.40