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 $51.92   3.254%   $53.6095   $53.61   $53.60   $53.60  
  Purchase #2 $226.70   11.866%   $253.6002   $253.60   $253.60   $253.60  
  Purchase #3 $244.42   4.165%   $254.6001   $254.60   $254.60   $254.60  
  Purchase #4 $101.78   7.765%   $109.6832   $109.68   $109.70   $109.70  
  Purchase #5 $134.63   5.333%   $141.8098   $141.81   $141.80   $141.80  
  Purchase #6 $183.29   7.684%   $197.374   $197.37   $197.35   $197.40  
  Purchase #7 $50.30   11.532%   $56.1006   $56.10   $56.10   $56.10  
  7 purchase totals = $993.04       $1,066.7774   $1,066.77   $1,066.75   $1,066.80