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	$18.98	6.595%	$20.2317	$20.23	$20.25	$20.20
Purchase #2	$83.62	5.235%	$87.9975	$88.00	$88.00	$88.00
Purchase #3	$110.69	11.568%	$123.4946	$123.49	$123.50	$123.50
Purchase #4	$205.67	8.668%	$223.4975	$223.50	$223.50	$223.50
Purchase #5	$134.69	3.494%	$139.3961	$139.40	$139.40	$139.40
Purchase #6	$225.35	13.431%	$255.6168	$255.62	$255.60	$255.60
Purchase #7	$41.76	4.207%	$43.5168	$43.52	$43.50	$43.50
7 purchase totals =	$820.76		$893.7510	$893.76	$893.75	$893.70