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 $216.95   6.129%   $230.2469   $230.25   $230.25   $230.20  
  Purchase #2 $191.90   11.708%   $214.3677   $214.37   $214.35   $214.40  
  Purchase #3 $14.59   4.336%   $15.2226   $15.22   $15.20   $15.20  
  Purchase #4 $144.95   11.299%   $161.3279   $161.33   $161.35   $161.30  
  Purchase #5 $132.54   13.337%   $150.2169   $150.22   $150.20   $150.20  
  Purchase #6 $205.77   13.664%   $233.8864   $233.89   $233.90   $233.90  
  Purchase #7 $30.49   5.293%   $32.1038   $32.10   $32.10   $32.10  
  7 purchase totals = $937.19       $1,037.3722   $1,037.38   $1,037.35   $1,037.30