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 $93.38   4.419%   $97.5065   $97.51   $97.50   $97.50  
  Purchase #2 $91.45   8.234%   $98.98   $98.98   $99.00   $99.00  
  Purchase #3 $127.35   4.178%   $132.6707   $132.67   $132.65   $132.70  
  Purchase #4 $49.79   9.659%   $54.5992   $54.60   $54.60   $54.60  
  Purchase #5 $120.81   8.133%   $130.6355   $130.64   $130.65   $130.60  
  Purchase #6 $78.51   7.425%   $84.3394   $84.34   $84.35   $84.30  
  Purchase #7 $178.95   9.829%   $196.539   $196.54   $196.55   $196.50  
  7 purchase totals = $740.24       $795.2703   $795.28   $795.30   $795.20