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 $191.36   13.679%   $217.5361   $217.54   $217.55   $217.50  
  Purchase #2 $24.52   11.651%   $27.3768   $27.38   $27.40   $27.40  
  Purchase #3 $231.44   13.448%   $262.5641   $262.56   $262.55   $262.60  
  Purchase #4 $187.47   11.348%   $208.7441   $208.74   $208.75   $208.70  
  Purchase #5 $100.87   3.468%   $104.3682   $104.37   $104.35   $104.40  
  Purchase #6 $101.89   5.515%   $107.5092   $107.51   $107.50   $107.50  
  Purchase #7 $130.94   7.379%   $140.6021   $140.60   $140.60   $140.60  
  7 purchase totals = $968.49       $1,068.7006   $1,068.70   $1,068.70   $1,068.70