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 $129.30   10.862%   $143.3446   $143.34   $143.35   $143.30  
  Purchase #2 $185.94   5.521%   $196.2057   $196.21   $196.20   $196.20  
  Purchase #3 $232.38   10.722%   $257.2958   $257.30   $257.30   $257.30  
  Purchase #4 $245.99   4.645%   $257.4162   $257.42   $257.40   $257.40  
  Purchase #5 $189.70   12.500%   $213.4125   $213.41   $213.40   $213.40  
  Purchase #6 $151.42   11.352%   $168.6092   $168.61   $168.60   $168.60  
  Purchase #7 $16.26   12.763%   $18.3353   $18.34   $18.35   $18.30  
  7 purchase totals = $1,150.99       $1,254.6193   $1,254.63   $1,254.60   $1,254.50