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 $224.87   7.283%   $241.2473   $241.25   $241.25   $241.20  
  Purchase #2 $211.79   4.503%   $221.3269   $221.33   $221.35   $221.30  
  Purchase #3 $237.47   5.261%   $249.9633   $249.96   $249.95   $250.00  
  Purchase #4 $9.66   4.546%   $10.0991   $10.10   $10.10   $10.10  
  Purchase #5 $174.91   7.851%   $188.6422   $188.64   $188.65   $188.60  
  Purchase #6 $46.25   11.279%   $51.4665   $51.47   $51.45   $51.50  
  Purchase #7 $46.82   5.157%   $49.2345   $49.23   $49.25   $49.20  
  7 purchase totals = $951.77       $1,011.9798   $1,011.98   $1,012.00   $1,011.90