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 $44.45   10.183%   $48.9763   $48.98   $49.00   $49.00  
  Purchase #2 $206.82   4.608%   $216.3503   $216.35   $216.35   $216.40  
  Purchase #3 $118.91   12.480%   $133.75   $133.75   $133.75   $133.80  
  Purchase #4 $89.87   5.525%   $94.8353   $94.84   $94.85   $94.80  
  Purchase #5 $226.28   9.714%   $248.2608   $248.26   $248.25   $248.30  
  Purchase #6 $16.38   7.802%   $17.658   $17.66   $17.65   $17.70  
  Purchase #7 $54.26   8.818%   $59.0446   $59.04   $59.05   $59.00  
  7 purchase totals = $756.97       $818.8753   $818.88   $818.90   $819.00