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	$207.86	6.662%	$221.7076	$221.71	$221.70	$221.70
Purchase #2	$73.71	13.444%	$83.6196	$83.62	$83.60	$83.60
Purchase #3	$150.47	9.809%	$165.2296	$165.23	$165.25	$165.20
Purchase #4	$194.54	10.254%	$214.4881	$214.49	$214.50	$214.50
Purchase #5	$99.49	9.676%	$109.1167	$109.12	$109.10	$109.10
Purchase #6	$220.50	13.146%	$249.4869	$249.49	$249.50	$249.50
Purchase #7	$141.74	4.311%	$147.8504	$147.85	$147.85	$147.90
7 purchase totals =	$1,088.31		$1,191.4989	$1,191.51	$1,191.50	$1,191.50