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	$243.68	9.254%	$266.2301	$266.23	$266.25	$266.20
Purchase #2	$146.84	3.163%	$151.4845	$151.48	$151.50	$151.50
Purchase #3	$35.74	9.263%	$39.0506	$39.05	$39.05	$39.10
Purchase #4	$205.84	6.652%	$219.5325	$219.53	$219.55	$219.50
Purchase #5	$199.96	13.178%	$226.3107	$226.31	$226.30	$226.30
Purchase #6	$235.82	8.340%	$255.4874	$255.49	$255.50	$255.50
Purchase #7	$134.92	5.331%	$142.1126	$142.11	$142.10	$142.10
7 purchase totals =	$1,202.80		$1,300.2084	$1,300.20	$1,300.25	$1,300.20