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 $53.98   5.139%   $56.754   $56.75   $56.75   $56.80  
  Purchase #2 $87.47   9.756%   $96.0036   $96.00   $96.00   $96.00  
  Purchase #3 $201.75   11.751%   $225.4576   $225.46   $225.45   $225.50  
  Purchase #4 $208.40   3.103%   $214.8667   $214.87   $214.85   $214.90  
  Purchase #5 $130.44   8.640%   $141.71   $141.71   $141.70   $141.70  
  Purchase #6 $113.58   3.186%   $117.1987   $117.20   $117.20   $117.20  
  Purchase #7 $131.36   6.182%   $139.4807   $139.48   $139.50   $139.50  
  7 purchase totals = $926.98       $991.4713   $991.47   $991.45   $991.60