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 $206.29   8.663%   $224.1609   $224.16   $224.15   $224.20  
  Purchase #2 $165.57   9.348%   $181.0475   $181.05   $181.05   $181.00  
  Purchase #3 $18.86   7.533%   $20.2807   $20.28   $20.30   $20.30  
  Purchase #4 $46.62   6.817%   $49.7981   $49.80   $49.80   $49.80  
  Purchase #5 $21.95   10.663%   $24.2905   $24.29   $24.30   $24.30  
  Purchase #6 $218.44   8.283%   $236.5334   $236.53   $236.55   $236.50  
  Purchase #7 $100.89   12.231%   $113.2299   $113.23   $113.25   $113.20  
  7 purchase totals = $778.62       $849.3410   $849.34   $849.40   $849.30