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 $62.66   5.543%   $66.1332   $66.13   $66.15   $66.10  
  Purchase #2 $180.95   12.792%   $204.0971   $204.10   $204.10   $204.10  
  Purchase #3 $50.31   8.228%   $54.4495   $54.45   $54.45   $54.40  
  Purchase #4 $23.77   3.519%   $24.6065   $24.61   $24.60   $24.60  
  Purchase #5 $12.70   11.520%   $14.163   $14.16   $14.15   $14.20  
  Purchase #6 $250.26   12.305%   $281.0545   $281.05   $281.05   $281.10  
  Purchase #7 $237.37   12.705%   $267.5279   $267.53   $267.55   $267.50  
  7 purchase totals = $818.02       $912.0317   $912.03   $912.05   $912.00