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 $209.44   7.569%   $225.2925   $225.29   $225.30   $225.30  
  Purchase #2 $157.87   11.223%   $175.5878   $175.59   $175.60   $175.60  
  Purchase #3 $138.63   8.281%   $150.11   $150.11   $150.10   $150.10  
  Purchase #4 $183.88   11.400%   $204.8423   $204.84   $204.85   $204.80  
  Purchase #5 $85.66   8.468%   $92.9137   $92.91   $92.90   $92.90  
  Purchase #6 $22.84   12.446%   $25.6827   $25.68   $25.70   $25.70  
  Purchase #7 $28.29   8.136%   $30.5917   $30.59   $30.60   $30.60  
  7 purchase totals = $826.61       $905.0207   $905.01   $905.05   $905.00