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 $55.79   7.569%   $60.0127   $60.01   $60.00   $60.00  
  Purchase #2 $124.49   13.677%   $141.5165   $141.52   $141.50   $141.50  
  Purchase #3 $229.93   5.117%   $241.6955   $241.70   $241.70   $241.70  
  Purchase #4 $89.68   4.516%   $93.7299   $93.73   $93.75   $93.70  
  Purchase #5 $50.50   8.469%   $54.7768   $54.78   $54.80   $54.80  
  Purchase #6 $238.74   6.492%   $254.239   $254.24   $254.25   $254.20  
  Purchase #7 $55.76   8.399%   $60.4433   $60.44   $60.45   $60.40  
  7 purchase totals = $844.89       $906.4137   $906.42   $906.45   $906.30