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 $94.34   7.798%   $101.6966   $101.70   $101.70   $101.70  
  Purchase #2 $148.84   12.205%   $167.0059   $167.01   $167.00   $167.00  
  Purchase #3 $44.39   3.783%   $46.0693   $46.07   $46.05   $46.10  
  Purchase #4 $102.53   11.626%   $114.4501   $114.45   $114.45   $114.50  
  Purchase #5 $220.75   8.840%   $240.2643   $240.26   $240.25   $240.30  
  Purchase #6 $50.77   5.679%   $53.6532   $53.65   $53.65   $53.70  
  Purchase #7 $38.84   11.202%   $43.1909   $43.19   $43.20   $43.20  
  7 purchase totals = $700.46       $766.3303   $766.33   $766.30   $766.50