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 $53.83   10.610%   $59.5414   $59.54   $59.55   $59.50  
  Purchase #2 $25.35   11.723%   $28.3218   $28.32   $28.30   $28.30  
  Purchase #3 $148.29   13.268%   $167.9651   $167.97   $167.95   $168.00  
  Purchase #4 $21.34   10.131%   $23.502   $23.50   $23.50   $23.50  
  Purchase #5 $233.35   8.866%   $254.0388   $254.04   $254.05   $254.00  
  Purchase #6 $69.94   13.169%   $79.1504   $79.15   $79.15   $79.20  
  Purchase #7 $135.40   13.265%   $153.3608   $153.36   $153.35   $153.40  
  7 purchase totals = $687.50       $765.8803   $765.88   $765.85   $765.90