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	$212.25	4.281%	$221.3364	$221.34	$221.35	$221.30
Purchase #2	$150.72	6.184%	$160.0405	$160.04	$160.05	$160.00
Purchase #3	$150.38	4.496%	$157.1411	$157.14	$157.15	$157.10
Purchase #4	$69.43	5.729%	$73.4076	$73.41	$73.40	$73.40
Purchase #5	$28.88	13.380%	$32.7441	$32.74	$32.75	$32.70
Purchase #6	$167.34	11.461%	$186.5188	$186.52	$186.50	$186.50
Purchase #7	$53.76	9.874%	$59.0683	$59.07	$59.05	$59.10
7 purchase totals =	$832.76		$890.2568	$890.26	$890.25	$890.10