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 $24.65   3.679%   $25.5569   $25.56   $25.55   $25.60  
  Purchase #2 $116.44   7.361%   $125.0111   $125.01   $125.00   $125.00  
  Purchase #3 $177.92   12.140%   $199.5195   $199.52   $199.50   $199.50  
  Purchase #4 $208.91   8.516%   $226.7008   $226.70   $226.70   $226.70  
  Purchase #5 $200.98   8.151%   $217.3619   $217.36   $217.35   $217.40  
  Purchase #6 $37.85   9.566%   $41.4707   $41.47   $41.45   $41.50  
  Purchase #7 $166.53   7.105%   $178.362   $178.36   $178.35   $178.40  
  7 purchase totals = $933.28       $1,013.9829   $1,013.98   $1,013.90   $1,014.10