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 $219.45   5.698%   $231.9543   $231.95   $231.95   $232.00  
  Purchase #2 $50.50   6.318%   $53.6906   $53.69   $53.70   $53.70  
  Purchase #3 $190.63   11.342%   $212.2513   $212.25   $212.25   $212.30  
  Purchase #4 $86.87   9.624%   $95.2304   $95.23   $95.25   $95.20  
  Purchase #5 $158.74   7.326%   $170.3693   $170.37   $170.35   $170.40  
  Purchase #6 $102.81   9.390%   $112.4639   $112.46   $112.45   $112.50  
  Purchase #7 $120.50   11.806%   $134.7262   $134.73   $134.75   $134.70  
  7 purchase totals = $929.50       $1,010.6860   $1,010.68   $1,010.70   $1,010.80