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 $54.63   13.701%   $62.1149   $62.11   $62.10   $62.10  
  Purchase #2 $138.87   12.399%   $156.0885   $156.09   $156.10   $156.10  
  Purchase #3 $117.34   11.851%   $131.246   $131.25   $131.25   $131.20  
  Purchase #4 $44.36   4.726%   $46.4565   $46.46   $46.45   $46.50  
  Purchase #5 $113.63   7.409%   $122.0488   $122.05   $122.05   $122.00  
  Purchase #6 $175.76   13.659%   $199.7671   $199.77   $199.75   $199.80  
  Purchase #7 $23.38   7.411%   $25.1127   $25.11   $25.10   $25.10  
  7 purchase totals = $667.97       $742.8345   $742.84   $742.80   $742.80