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 $15.98   6.109%   $16.9562   $16.96   $16.95   $17.00  
  Purchase #2 $67.51   8.805%   $73.4543   $73.45   $73.45   $73.50  
  Purchase #3 $75.41   6.836%   $80.565   $80.57   $80.55   $80.60  
  Purchase #4 $240.80   10.533%   $266.1635   $266.16   $266.15   $266.20  
  Purchase #5 $187.36   9.749%   $205.6257   $205.63   $205.65   $205.60  
  Purchase #6 $224.27   12.246%   $251.7341   $251.73   $251.75   $251.70  
  Purchase #7 $55.27   5.837%   $58.4961   $58.50   $58.50   $58.50  
  7 purchase totals = $866.60       $952.9949   $953.00   $953.00   $953.10