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	$67.93	7.350%	$72.9229	$72.92	$72.90	$72.90
Purchase #2	$16.72	10.421%	$18.4624	$18.46	$18.45	$18.50
Purchase #3	$216.69	4.847%	$227.193	$227.19	$227.20	$227.20
Purchase #4	$7.26	5.462%	$7.6565	$7.66	$7.65	$7.70
Purchase #5	$15.98	6.167%	$16.9655	$16.97	$16.95	$17.00
Purchase #6	$93.59	7.674%	$100.7721	$100.77	$100.75	$100.80
Purchase #7	$122.39	12.238%	$137.3681	$137.37	$137.35	$137.40
7 purchase totals =	$540.56		$581.3405	$581.34	$581.25	$581.50