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 $119.67   11.771%   $133.7564   $133.76   $133.75   $133.80  
  Purchase #2 $103.63   6.690%   $110.5628   $110.56   $110.55   $110.60  
  Purchase #3 $110.36   13.259%   $124.9926   $124.99   $125.00   $125.00  
  Purchase #4 $96.71   11.843%   $108.1634   $108.16   $108.15   $108.20  
  Purchase #5 $84.58   5.593%   $89.3106   $89.31   $89.30   $89.30  
  Purchase #6 $57.74   5.414%   $60.866   $60.87   $60.85   $60.90  
  Purchase #7 $194.73   5.686%   $205.8023   $205.80   $205.80   $205.80  
  7 purchase totals = $767.42       $833.4541   $833.45   $833.40   $833.60