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 $126.28   11.756%   $141.1255   $141.13   $141.15   $141.10  
  Purchase #2 $15.52   6.674%   $16.5558   $16.56   $16.55   $16.60  
  Purchase #3 $102.56   7.656%   $110.412   $110.41   $110.40   $110.40  
  Purchase #4 $89.27   12.363%   $100.3065   $100.31   $100.30   $100.30  
  Purchase #5 $208.42   10.391%   $230.0769   $230.08   $230.10   $230.10  
  Purchase #6 $46.55   3.163%   $48.0224   $48.02   $48.00   $48.00  
  Purchase #7 $80.54   7.259%   $86.3864   $86.39   $86.40   $86.40  
  7 purchase totals = $669.14       $732.8855   $732.90   $732.90   $732.90