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	$73.96	13.175%	$83.7042	$83.70	$83.70	$83.70
Purchase #2	$33.88	3.793%	$35.1651	$35.17	$35.15	$35.20
Purchase #3	$83.76	4.847%	$87.8198	$87.82	$87.80	$87.80
Purchase #4	$77.78	10.822%	$86.1974	$86.20	$86.20	$86.20
Purchase #5	$236.25	5.495%	$249.2319	$249.23	$249.25	$249.20
Purchase #6	$103.26	7.769%	$111.2823	$111.28	$111.30	$111.30
Purchase #7	$139.67	9.452%	$152.8716	$152.87	$152.85	$152.90
7 purchase totals =	$748.56		$806.2723	$806.27	$806.25	$806.30