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	$89.34	12.335%	$100.3601	$100.36	$100.35	$100.40
Purchase #2	$127.41	5.784%	$134.7794	$134.78	$134.80	$134.80
Purchase #3	$124.58	13.418%	$141.2961	$141.30	$141.30	$141.30
Purchase #4	$218.52	7.515%	$234.9418	$234.94	$234.95	$234.90
Purchase #5	$18.94	6.371%	$20.1467	$20.15	$20.15	$20.10
Purchase #6	$94.83	11.476%	$105.7127	$105.71	$105.70	$105.70
Purchase #7	$81.85	11.318%	$91.1138	$91.11	$91.10	$91.10
7 purchase totals =	$755.47		$828.3506	$828.35	$828.35	$828.30