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	$38.50	4.531%	$40.2444	$40.24	$40.25	$40.20
Purchase #2	$44.95	12.783%	$50.696	$50.70	$50.70	$50.70
Purchase #3	$35.51	4.558%	$37.1285	$37.13	$37.15	$37.10
Purchase #4	$13.40	6.474%	$14.2675	$14.27	$14.25	$14.30
Purchase #5	$212.87	7.302%	$228.4138	$228.41	$228.40	$228.40
Purchase #6	$83.68	7.348%	$89.8288	$89.83	$89.85	$89.80
Purchase #7	$53.63	10.712%	$59.3748	$59.37	$59.35	$59.40
7 purchase totals =	$482.54		$519.9538	$519.95	$519.95	$519.90