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 $121.96   5.685%   $128.8934   $128.89   $128.90   $128.90  
  Purchase #2 $74.27   12.682%   $83.6889   $83.69   $83.70   $83.70  
  Purchase #3 $37.62   6.818%   $40.1849   $40.18   $40.20   $40.20  
  Purchase #4 $15.56   8.858%   $16.9383   $16.94   $16.95   $16.90  
  Purchase #5 $63.30   9.673%   $69.423   $69.42   $69.40   $69.40  
  Purchase #6 $13.38   13.485%   $15.1843   $15.18   $15.20   $15.20  
  Purchase #7 $125.43   3.377%   $129.6658   $129.67   $129.65   $129.70  
  7 purchase totals = $451.52       $483.9786   $483.97   $484.00   $484.00