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 $34.60   7.421%   $37.1677   $37.17   $37.15   $37.20  
  Purchase #2 $215.85   11.103%   $239.8158   $239.82   $239.80   $239.80  
  Purchase #3 $197.90   5.252%   $208.2937   $208.29   $208.30   $208.30  
  Purchase #4 $79.53   11.683%   $88.8215   $88.82   $88.80   $88.80  
  Purchase #5 $92.90   5.456%   $97.9686   $97.97   $97.95   $98.00  
  Purchase #6 $23.66   3.626%   $24.5179   $24.52   $24.50   $24.50  
  Purchase #7 $92.62   4.324%   $96.6249   $96.62   $96.60   $96.60  
  7 purchase totals = $737.06       $793.2101   $793.21   $793.10   $793.20