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 $7.53   10.259%   $8.3025   $8.30   $8.30   $8.30  
  Purchase #2 $191.44   6.716%   $204.2971   $204.30   $204.30   $204.30  
  Purchase #3 $199.75   4.419%   $208.577   $208.58   $208.60   $208.60  
  Purchase #4 $232.41   6.222%   $246.8706   $246.87   $246.85   $246.90  
  Purchase #5 $98.95   9.763%   $108.6105   $108.61   $108.60   $108.60  
  Purchase #6 $45.64   9.561%   $50.0036   $50.00   $50.00   $50.00  
  Purchase #7 $119.39   5.379%   $125.812   $125.81   $125.80   $125.80  
  7 purchase totals = $895.11       $952.4733   $952.47   $952.45   $952.50