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 $146.78   4.232%   $152.9917   $152.99   $153.00   $153.00  
  Purchase #2 $192.93   5.397%   $203.3424   $203.34   $203.35   $203.30  
  Purchase #3 $14.81   13.262%   $16.7741   $16.77   $16.75   $16.80  
  Purchase #4 $54.67   12.579%   $61.5469   $61.55   $61.55   $61.50  
  Purchase #5 $42.93   7.204%   $46.0227   $46.02   $46.00   $46.00  
  Purchase #6 $78.76   10.610%   $87.1164   $87.12   $87.10   $87.10  
  Purchase #7 $210.83   6.408%   $224.34   $224.34   $224.35   $224.30  
  7 purchase totals = $741.71       $792.1342   $792.13   $792.10   $792.00