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 $23.36   8.150%   $25.2638   $25.26   $25.25   $25.30  
  Purchase #2 $250.53   4.814%   $262.5905   $262.59   $262.60   $262.60  
  Purchase #3 $148.98   7.545%   $160.2205   $160.22   $160.20   $160.20  
  Purchase #4 $109.88   12.654%   $123.7842   $123.78   $123.80   $123.80  
  Purchase #5 $12.94   5.745%   $13.6834   $13.68   $13.70   $13.70  
  Purchase #6 $203.63   4.796%   $213.3961   $213.40   $213.40   $213.40  
  Purchase #7 $146.99   11.475%   $163.8571   $163.86   $163.85   $163.90  
  7 purchase totals = $896.31       $962.7956   $962.79   $962.80   $962.90