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 $69.79   7.474%   $75.0061   $75.01   $75.00   $75.00  
  Purchase #2 $130.63   13.793%   $148.6478   $148.65   $148.65   $148.60  
  Purchase #3 $248.42   9.858%   $272.9092   $272.91   $272.90   $272.90  
  Purchase #4 $49.68   4.434%   $51.8828   $51.88   $51.90   $51.90  
  Purchase #5 $116.34   12.774%   $131.2013   $131.20   $131.20   $131.20  
  Purchase #6 $54.73   8.429%   $59.3432   $59.34   $59.35   $59.30  
  Purchase #7 $97.44   13.171%   $110.2738   $110.27   $110.25   $110.30  
  7 purchase totals = $767.03       $849.2642   $849.26   $849.25   $849.20