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 $54.32   11.123%   $60.362   $60.36   $60.35   $60.40  
  Purchase #2 $187.96   3.203%   $193.9804   $193.98   $194.00   $194.00  
  Purchase #3 $178.33   13.445%   $202.3065   $202.31   $202.30   $202.30  
  Purchase #4 $159.38   10.481%   $176.0846   $176.08   $176.10   $176.10  
  Purchase #5 $179.78   4.126%   $187.1977   $187.20   $187.20   $187.20  
  Purchase #6 $46.98   9.778%   $51.5737   $51.57   $51.55   $51.60  
  Purchase #7 $158.86   13.664%   $180.5666   $180.57   $180.55   $180.60  
  7 purchase totals = $965.61       $1,052.0715   $1,052.07   $1,052.05   $1,052.20