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	$132.32	5.716%	$139.8834	$139.88	$139.90	$139.90
Purchase #2	$16.29	10.842%	$18.0562	$18.06	$18.05	$18.10
Purchase #3	$66.34	7.491%	$71.3095	$71.31	$71.30	$71.30
Purchase #4	$241.80	13.790%	$275.1442	$275.14	$275.15	$275.10
Purchase #5	$215.53	12.480%	$242.4281	$242.43	$242.45	$242.40
Purchase #6	$12.56	9.543%	$13.7586	$13.76	$13.75	$13.80
Purchase #7	$73.65	9.559%	$80.6902	$80.69	$80.70	$80.70
7 purchase totals =	$758.49		$841.2702	$841.27	$841.30	$841.30