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 $45.31   3.153%   $46.7386   $46.74   $46.75   $46.70  
  Purchase #2 $234.40   13.213%   $265.3713   $265.37   $265.35   $265.40  
  Purchase #3 $117.54   5.833%   $124.3961   $124.40   $124.40   $124.40  
  Purchase #4 $87.86   12.267%   $98.6378   $98.64   $98.65   $98.60  
  Purchase #5 $133.54   4.451%   $139.4839   $139.48   $139.50   $139.50  
  Purchase #6 $33.69   10.747%   $37.3107   $37.31   $37.30   $37.30  
  Purchase #7 $186.27   10.569%   $205.9569   $205.96   $205.95   $206.00  
  7 purchase totals = $838.61       $917.8953   $917.90   $917.90   $917.90