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 $74.94   11.680%   $83.693   $83.69   $83.70   $83.70  
  Purchase #2 $149.25   7.573%   $160.5527   $160.55   $160.55   $160.60  
  Purchase #3 $149.83   9.634%   $164.2646   $164.26   $164.25   $164.30  
  Purchase #4 $243.57   12.380%   $273.724   $273.72   $273.70   $273.70  
  Purchase #5 $164.88   9.707%   $180.8849   $180.88   $180.90   $180.90  
  Purchase #6 $129.36   4.172%   $134.7569   $134.76   $134.75   $134.80  
  Purchase #7 $200.51   13.733%   $228.046   $228.05   $228.05   $228.00  
  7 purchase totals = $1,112.34       $1,225.9221   $1,225.91   $1,225.90   $1,226.00