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	$35.47	9.797%	$38.945	$38.95	$38.95	$38.90
Purchase #2	$119.62	9.401%	$130.8655	$130.87	$130.85	$130.90
Purchase #3	$91.41	9.804%	$100.3718	$100.37	$100.35	$100.40
Purchase #4	$133.70	11.578%	$149.1798	$149.18	$149.20	$149.20
Purchase #5	$223.43	13.783%	$254.2254	$254.23	$254.25	$254.20
Purchase #6	$136.72	8.605%	$148.4848	$148.48	$148.50	$148.50
Purchase #7	$167.65	13.592%	$190.437	$190.44	$190.45	$190.40
7 purchase totals =	$908.00		$1,012.5093	$1,012.52	$1,012.55	$1,012.50