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 $187.61   5.246%   $197.452   $197.45   $197.45   $197.50  
  Purchase #2 $55.44   12.351%   $62.2874   $62.29   $62.30   $62.30  
  Purchase #3 $65.31   7.138%   $69.9718   $69.97   $69.95   $70.00  
  Purchase #4 $75.86   8.604%   $82.387   $82.39   $82.40   $82.40  
  Purchase #5 $136.46   9.616%   $149.582   $149.58   $149.60   $149.60  
  Purchase #6 $219.51   13.494%   $249.1307   $249.13   $249.15   $249.10  
  Purchase #7 $57.98   4.728%   $60.7213   $60.72   $60.70   $60.70  
  7 purchase totals = $798.17       $871.5322   $871.53   $871.55   $871.60