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 $182.60   8.773%   $198.6195   $198.62   $198.60   $198.60  
  Purchase #2 $118.43   10.158%   $130.4601   $130.46   $130.45   $130.50  
  Purchase #3 $100.48   12.495%   $113.035   $113.04   $113.05   $113.00  
  Purchase #4 $67.69   8.515%   $73.4538   $73.45   $73.45   $73.50  
  Purchase #5 $46.98   9.355%   $51.375   $51.38   $51.40   $51.40  
  Purchase #6 $92.38   9.640%   $101.2854   $101.29   $101.30   $101.30  
  Purchase #7 $104.79   13.245%   $118.6694   $118.67   $118.65   $118.70  
  7 purchase totals = $713.35       $786.8982   $786.91   $786.90   $787.00