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 $184.90   11.651%   $206.4427   $206.44   $206.45   $206.40  
  Purchase #2 $237.68   7.596%   $255.7342   $255.73   $255.75   $255.70  
  Purchase #3 $103.82   11.806%   $116.077   $116.08   $116.10   $116.10  
  Purchase #4 $145.25   12.752%   $163.7723   $163.77   $163.75   $163.80  
  Purchase #5 $112.76   12.124%   $126.431   $126.43   $126.45   $126.40  
  Purchase #6 $207.44   8.360%   $224.782   $224.78   $224.80   $224.80  
  Purchase #7 $239.39   5.766%   $253.1932   $253.19   $253.20   $253.20  
  7 purchase totals = $1,231.24       $1,346.4324   $1,346.42   $1,346.50   $1,346.40