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 $225.34   9.243%   $246.1682   $246.17   $246.15   $246.20  
  Purchase #2 $111.78   13.309%   $126.6568   $126.66   $126.65   $126.70  
  Purchase #3 $160.61   13.151%   $181.7318   $181.73   $181.75   $181.70  
  Purchase #4 $49.75   7.296%   $53.3798   $53.38   $53.40   $53.40  
  Purchase #5 $144.96   5.209%   $152.511   $152.51   $152.50   $152.50  
  Purchase #6 $141.88   6.526%   $151.1391   $151.14   $151.15   $151.10  
  Purchase #7 $48.32   11.730%   $53.9879   $53.99   $54.00   $54.00  
  7 purchase totals = $882.64       $965.5746   $965.58   $965.60   $965.60