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 $170.68   13.755%   $194.157   $194.16   $194.15   $194.20  
  Purchase #2 $236.92   7.846%   $255.5087   $255.51   $255.50   $255.50  
  Purchase #3 $162.88   9.362%   $178.1288   $178.13   $178.15   $178.10  
  Purchase #4 $203.97   10.190%   $224.7545   $224.75   $224.75   $224.80  
  Purchase #5 $36.51   3.199%   $37.678   $37.68   $37.70   $37.70  
  Purchase #6 $221.78   3.510%   $229.5645   $229.56   $229.55   $229.60  
  Purchase #7 $79.65   10.770%   $88.2283   $88.23   $88.25   $88.20  
  7 purchase totals = $1,112.39       $1,208.0198   $1,208.02   $1,208.05   $1,208.10