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 $163.97   10.718%   $181.5443   $181.54   $181.55   $181.50  
  Purchase #2 $233.38   4.597%   $244.1085   $244.11   $244.10   $244.10  
  Purchase #3 $158.42   8.186%   $171.3883   $171.39   $171.40   $171.40  
  Purchase #4 $62.76   10.231%   $69.181   $69.18   $69.20   $69.20  
  Purchase #5 $111.86   5.397%   $117.8971   $117.90   $117.90   $117.90  
  Purchase #6 $161.77   12.143%   $181.4137   $181.41   $181.40   $181.40  
  Purchase #7 $54.51   6.843%   $58.2401   $58.24   $58.25   $58.20  
  7 purchase totals = $946.67       $1,023.7730   $1,023.77   $1,023.80   $1,023.70