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 $56.86   8.175%   $61.5083   $61.51   $61.50   $61.50  
  Purchase #2 $14.30   13.630%   $16.2491   $16.25   $16.25   $16.20  
  Purchase #3 $200.63   8.352%   $217.3866   $217.39   $217.40   $217.40  
  Purchase #4 $244.91   4.549%   $256.051   $256.05   $256.05   $256.10  
  Purchase #5 $61.52   9.554%   $67.3976   $67.40   $67.40   $67.40  
  Purchase #6 $166.78   5.296%   $175.6127   $175.61   $175.60   $175.60  
  Purchase #7 $56.74   7.109%   $60.7736   $60.77   $60.75   $60.80  
  7 purchase totals = $801.74       $854.9789   $854.98   $854.95   $855.00