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	$234.67	12.180%	$263.2528	$263.25	$263.25	$263.30
Purchase #2	$136.83	11.428%	$152.4669	$152.47	$152.45	$152.50
Purchase #3	$104.70	3.622%	$108.4922	$108.49	$108.50	$108.50
Purchase #4	$174.69	12.360%	$196.2817	$196.28	$196.30	$196.30
Purchase #5	$220.86	12.454%	$248.3659	$248.37	$248.35	$248.40
Purchase #6	$245.83	7.615%	$264.55	$264.55	$264.55	$264.60
Purchase #7	$112.39	9.231%	$122.7647	$122.76	$122.75	$122.80
7 purchase totals =	$1,229.97		$1,356.1742	$1,356.17	$1,356.15	$1,356.40