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 $194.65   5.763%   $205.8677   $205.87   $205.85   $205.90  
  Purchase #2 $56.67   9.414%   $62.0049   $62.00   $62.00   $62.00  
  Purchase #3 $64.75   5.290%   $68.1753   $68.18   $68.20   $68.20  
  Purchase #4 $163.44   12.701%   $184.1985   $184.20   $184.20   $184.20  
  Purchase #5 $140.70   12.546%   $158.3522   $158.35   $158.35   $158.40  
  Purchase #6 $99.27   3.874%   $103.1157   $103.12   $103.10   $103.10  
  Purchase #7 $92.65   5.187%   $97.4558   $97.46   $97.45   $97.50  
  7 purchase totals = $812.13       $879.1701   $879.18   $879.15   $879.30