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	$235.73	8.482%	$255.7246	$255.72	$255.70	$255.70
Purchase #2	$149.83	13.502%	$170.06	$170.06	$170.05	$170.10
Purchase #3	$82.62	12.358%	$92.8302	$92.83	$92.85	$92.80
Purchase #4	$141.35	6.299%	$150.2536	$150.25	$150.25	$150.30
Purchase #5	$201.92	9.578%	$221.2599	$221.26	$221.25	$221.30
Purchase #6	$34.90	11.377%	$38.8706	$38.87	$38.85	$38.90
Purchase #7	$42.57	3.124%	$43.8999	$43.90	$43.90	$43.90
7 purchase totals =	$888.92		$972.8988	$972.89	$972.85	$973.00