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 $71.33   6.580%   $76.0235   $76.02   $76.00   $76.00  
  Purchase #2 $249.71   6.488%   $265.9112   $265.91   $265.90   $265.90  
  Purchase #3 $200.82   8.141%   $217.1688   $217.17   $217.15   $217.20  
  Purchase #4 $33.79   4.561%   $35.3312   $35.33   $35.35   $35.30  
  Purchase #5 $215.90   11.474%   $240.6724   $240.67   $240.65   $240.70  
  Purchase #6 $88.26   11.825%   $98.6967   $98.70   $98.70   $98.70  
  Purchase #7 $104.29   9.272%   $113.9598   $113.96   $113.95   $114.00  
  7 purchase totals = $964.10       $1,047.7636   $1,047.76   $1,047.70   $1,047.80