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	$71.47	4.194%	$74.4675	$74.47	$74.45	$74.50
Purchase #2	$23.95	10.838%	$26.5457	$26.55	$26.55	$26.50
Purchase #3	$99.34	9.202%	$108.4813	$108.48	$108.50	$108.50
Purchase #4	$91.29	10.507%	$100.8818	$100.88	$100.90	$100.90
Purchase #5	$153.72	12.355%	$172.7121	$172.71	$172.70	$172.70
Purchase #6	$242.70	11.696%	$271.0862	$271.09	$271.10	$271.10
Purchase #7	$77.91	7.538%	$83.7829	$83.78	$83.80	$83.80
7 purchase totals =	$760.38		$837.9575	$837.96	$838.00	$838.00