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 $213.94   12.851%   $241.4334   $241.43   $241.45   $241.40  
  Purchase #2 $98.34   11.537%   $109.6855   $109.69   $109.70   $109.70  
  Purchase #3 $215.58   6.665%   $229.9484   $229.95   $229.95   $229.90  
  Purchase #4 $36.89   6.106%   $39.1425   $39.14   $39.15   $39.10  
  Purchase #5 $249.68   11.392%   $278.1235   $278.12   $278.10   $278.10  
  Purchase #6 $101.95   4.188%   $106.2197   $106.22   $106.20   $106.20  
  Purchase #7 $57.89   4.302%   $60.3804   $60.38   $60.40   $60.40  
  7 purchase totals = $974.27       $1,064.9334   $1,064.93   $1,064.95   $1,064.80