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 $93.33   8.511%   $101.2733   $101.27   $101.25   $101.30  
  Purchase #2 $47.26   7.672%   $50.8858   $50.89   $50.90   $50.90  
  Purchase #3 $75.25   9.642%   $82.5056   $82.51   $82.50   $82.50  
  Purchase #4 $191.77   11.415%   $213.6605   $213.66   $213.65   $213.70  
  Purchase #5 $183.29   11.491%   $204.3519   $204.35   $204.35   $204.40  
  Purchase #6 $249.89   7.509%   $268.6542   $268.65   $268.65   $268.70  
  Purchase #7 $40.99   5.628%   $43.2969   $43.30   $43.30   $43.30  
  7 purchase totals = $881.78       $964.6282   $964.63   $964.60   $964.80