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	$204.40	9.216%	$223.2375	$223.24	$223.25	$223.20
Purchase #2	$33.68	3.562%	$34.8797	$34.88	$34.90	$34.90
Purchase #3	$219.40	9.721%	$240.7279	$240.73	$240.75	$240.70
Purchase #4	$33.92	4.417%	$35.4182	$35.42	$35.40	$35.40
Purchase #5	$104.83	6.188%	$111.3169	$111.32	$111.30	$111.30
Purchase #6	$85.75	4.657%	$89.7434	$89.74	$89.75	$89.70
Purchase #7	$76.45	10.344%	$84.358	$84.36	$84.35	$84.40
7 purchase totals =	$758.43		$819.6816	$819.69	$819.70	$819.60