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 $56.54   11.868%   $63.2502   $63.25   $63.25   $63.30  
  Purchase #2 $173.80   13.172%   $196.6929   $196.69   $196.70   $196.70  
  Purchase #3 $117.54   10.377%   $129.7371   $129.74   $129.75   $129.70  
  Purchase #4 $16.63   4.472%   $17.3737   $17.37   $17.35   $17.40  
  Purchase #5 $217.64   13.778%   $247.6264   $247.63   $247.65   $247.60  
  Purchase #6 $181.82   13.480%   $206.3293   $206.33   $206.35   $206.30  
  Purchase #7 $34.85   7.281%   $37.3874   $37.39   $37.40   $37.40  
  7 purchase totals = $798.82       $898.3970   $898.40   $898.45   $898.40