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 $70.63   6.754%   $75.4004   $75.40   $75.40   $75.40  
  Purchase #2 $153.85   5.268%   $161.9548   $161.95   $161.95   $162.00  
  Purchase #3 $215.85   8.303%   $233.772   $233.77   $233.75   $233.80  
  Purchase #4 $134.30   13.149%   $151.9591   $151.96   $151.95   $152.00  
  Purchase #5 $45.88   9.394%   $50.19   $50.19   $50.20   $50.20  
  Purchase #6 $82.30   6.566%   $87.7038   $87.70   $87.70   $87.70  
  Purchase #7 $202.71   5.797%   $214.4611   $214.46   $214.45   $214.50  
  7 purchase totals = $905.52       $975.4412   $975.43   $975.40   $975.60