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	$73.45	5.282%	$77.3296	$77.33	$77.35	$77.30
Purchase #2	$69.78	4.664%	$73.0345	$73.03	$73.05	$73.00
Purchase #3	$228.80	9.389%	$250.282	$250.28	$250.30	$250.30
Purchase #4	$76.87	10.675%	$85.0759	$85.08	$85.10	$85.10
Purchase #5	$64.27	11.365%	$71.5743	$71.57	$71.55	$71.60
Purchase #6	$34.73	11.482%	$38.7177	$38.72	$38.70	$38.70
Purchase #7	$131.50	12.766%	$148.2873	$148.29	$148.30	$148.30
7 purchase totals =	$679.40		$744.3013	$744.30	$744.35	$744.30