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 $149.26   9.549%   $163.5128   $163.51   $163.50   $163.50  
  Purchase #2 $111.78   9.588%   $122.4975   $122.50   $122.50   $122.50  
  Purchase #3 $223.42   6.767%   $238.5388   $238.54   $238.55   $238.50  
  Purchase #4 $153.47   4.447%   $160.2948   $160.29   $160.30   $160.30  
  Purchase #5 $101.48   11.492%   $113.1421   $113.14   $113.15   $113.10  
  Purchase #6 $23.56   11.662%   $26.3076   $26.31   $26.30   $26.30  
  Purchase #7 $29.94   7.484%   $32.1807   $32.18   $32.20   $32.20  
  7 purchase totals = $792.91       $856.4743   $856.47   $856.50   $856.40