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 $104.86   13.252%   $118.756   $118.76   $118.75   $118.80  
  Purchase #2 $172.37   11.102%   $191.5065   $191.51   $191.50   $191.50  
  Purchase #3 $158.69   12.132%   $177.9423   $177.94   $177.95   $177.90  
  Purchase #4 $201.66   8.708%   $219.2206   $219.22   $219.20   $219.20  
  Purchase #5 $231.49   9.694%   $253.9306   $253.93   $253.95   $253.90  
  Purchase #6 $112.34   6.204%   $119.3096   $119.31   $119.30   $119.30  
  Purchase #7 $42.75   8.416%   $46.3478   $46.35   $46.35   $46.30  
  7 purchase totals = $1,024.16       $1,127.0134   $1,127.02   $1,127.00   $1,126.90