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	$42.69	7.277%	$45.7966	$45.80	$45.80	$45.80
Purchase #2	$136.60	11.799%	$152.7174	$152.72	$152.70	$152.70
Purchase #3	$55.28	7.392%	$59.3663	$59.37	$59.35	$59.40
Purchase #4	$54.68	7.113%	$58.5694	$58.57	$58.55	$58.60
Purchase #5	$82.77	10.850%	$91.7505	$91.75	$91.75	$91.80
Purchase #6	$9.77	5.748%	$10.3316	$10.33	$10.35	$10.30
Purchase #7	$219.40	9.717%	$240.7191	$240.72	$240.70	$240.70
7 purchase totals =	$601.19		$659.2509	$659.26	$659.20	$659.30