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 $241.53   4.231%   $251.7491   $251.75   $251.75   $251.70  
  Purchase #2 $146.72   3.442%   $151.7701   $151.77   $151.75   $151.80  
  Purchase #3 $166.62   7.444%   $179.0232   $179.02   $179.00   $179.00  
  Purchase #4 $26.89   13.603%   $30.5478   $30.55   $30.55   $30.50  
  Purchase #5 $74.66   13.130%   $84.4629   $84.46   $84.45   $84.50  
  Purchase #6 $234.40   6.644%   $249.9735   $249.97   $249.95   $250.00  
  Purchase #7 $153.84   4.422%   $160.6428   $160.64   $160.65   $160.60  
  7 purchase totals = $1,044.66       $1,108.1694   $1,108.16   $1,108.10   $1,108.10