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	$22.28	8.209%	$24.109	$24.11	$24.10	$24.10
Purchase #2	$57.96	11.228%	$64.4677	$64.47	$64.45	$64.50
Purchase #3	$22.82	11.508%	$25.4461	$25.45	$25.45	$25.40
Purchase #4	$146.82	13.582%	$166.7611	$166.76	$166.75	$166.80
Purchase #5	$242.77	9.311%	$265.3743	$265.37	$265.35	$265.40
Purchase #6	$41.34	10.390%	$45.6352	$45.64	$45.65	$45.60
Purchase #7	$179.82	4.844%	$188.5305	$188.53	$188.55	$188.50
7 purchase totals =	$713.81		$780.3239	$780.33	$780.30	$780.30