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 $146.41   9.145%   $159.7992   $159.80   $159.80   $159.80  
  Purchase #2 $115.27   7.818%   $124.2818   $124.28   $124.30   $124.30  
  Purchase #3 $134.75   5.823%   $142.5965   $142.60   $142.60   $142.60  
  Purchase #4 $163.53   10.560%   $180.7988   $180.80   $180.80   $180.80  
  Purchase #5 $239.25   12.551%   $269.2783   $269.28   $269.30   $269.30  
  Purchase #6 $234.91   11.325%   $261.5136   $261.51   $261.50   $261.50  
  Purchase #7 $219.49   12.504%   $246.935   $246.94   $246.95   $246.90  
  7 purchase totals = $1,253.61       $1,385.2032   $1,385.21   $1,385.25   $1,385.20