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 $241.41   10.824%   $267.5402   $267.54   $267.55   $267.50  
  Purchase #2 $132.97   9.863%   $146.0848   $146.08   $146.10   $146.10  
  Purchase #3 $116.88   7.689%   $125.8669   $125.87   $125.85   $125.90  
  Purchase #4 $204.34   3.436%   $211.3611   $211.36   $211.35   $211.40  
  Purchase #5 $69.85   11.569%   $77.9309   $77.93   $77.95   $77.90  
  Purchase #6 $113.76   11.240%   $126.5466   $126.55   $126.55   $126.50  
  Purchase #7 $122.62   7.177%   $131.4204   $131.42   $131.40   $131.40  
  7 purchase totals = $1,001.83       $1,086.7509   $1,086.75   $1,086.75   $1,086.70