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	$159.89	5.559%	$168.7783	$168.78	$168.80	$168.80
Purchase #2	$57.94	7.731%	$62.4193	$62.42	$62.40	$62.40
Purchase #3	$47.77	11.726%	$53.3715	$53.37	$53.35	$53.40
Purchase #4	$124.26	4.707%	$130.1089	$130.11	$130.10	$130.10
Purchase #5	$167.48	8.523%	$181.7543	$181.75	$181.75	$181.80
Purchase #6	$141.39	8.130%	$152.885	$152.89	$152.90	$152.90
Purchase #7	$165.88	8.687%	$180.29	$180.29	$180.30	$180.30
7 purchase totals =	$864.61		$929.6073	$929.61	$929.60	$929.70