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 $189.44   13.216%   $214.4764   $214.48   $214.50   $214.50  
  Purchase #2 $167.75   13.221%   $189.9282   $189.93   $189.95   $189.90  
  Purchase #3 $238.90   7.520%   $256.8653   $256.87   $256.85   $256.90  
  Purchase #4 $181.95   4.560%   $190.2469   $190.25   $190.25   $190.20  
  Purchase #5 $182.36   12.201%   $204.6097   $204.61   $204.60   $204.60  
  Purchase #6 $24.25   5.324%   $25.5411   $25.54   $25.55   $25.50  
  Purchase #7 $214.45   3.608%   $222.1874   $222.19   $222.20   $222.20  
  7 purchase totals = $1,199.10       $1,303.8550   $1,303.87   $1,303.90   $1,303.80