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	$36.38	12.471%	$40.9169	$40.92	$40.90	$40.90
Purchase #2	$212.77	5.115%	$223.6532	$223.65	$223.65	$223.70
Purchase #3	$230.45	12.574%	$259.4268	$259.43	$259.45	$259.40
Purchase #4	$150.48	4.799%	$157.7015	$157.70	$157.70	$157.70
Purchase #5	$180.89	4.730%	$189.4461	$189.45	$189.45	$189.40
Purchase #6	$6.43	9.602%	$7.0474	$7.05	$7.05	$7.00
Purchase #7	$130.67	8.787%	$142.152	$142.15	$142.15	$142.20
7 purchase totals =	$948.07		$1,020.3439	$1,020.35	$1,020.35	$1,020.30