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 $156.88   6.726%   $167.4317   $167.43   $167.45   $167.40  
  Purchase #2 $61.32   4.835%   $64.2848   $64.28   $64.30   $64.30  
  Purchase #3 $205.26   5.752%   $217.0666   $217.07   $217.05   $217.10  
  Purchase #4 $98.33   9.160%   $107.337   $107.34   $107.35   $107.30  
  Purchase #5 $247.79   12.814%   $279.5418   $279.54   $279.55   $279.50  
  Purchase #6 $175.55   7.116%   $188.0421   $188.04   $188.05   $188.00  
  Purchase #7 $77.26   3.167%   $79.7068   $79.71   $79.70   $79.70  
  7 purchase totals = $1,022.39       $1,103.4108   $1,103.41   $1,103.45   $1,103.30