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	$171.64	10.474%	$189.6176	$189.62	$189.60	$189.60
Purchase #2	$238.48	8.772%	$259.3995	$259.40	$259.40	$259.40
Purchase #3	$101.76	8.168%	$110.0718	$110.07	$110.05	$110.10
Purchase #4	$12.98	5.852%	$13.7396	$13.74	$13.75	$13.70
Purchase #5	$128.75	12.143%	$144.3841	$144.38	$144.40	$144.40
Purchase #6	$78.89	5.821%	$83.4822	$83.48	$83.50	$83.50
Purchase #7	$250.92	9.642%	$275.1137	$275.11	$275.10	$275.10
7 purchase totals =	$983.42		$1,075.8085	$1,075.80	$1,075.80	$1,075.80