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	$66.31	10.201%	$73.0743	$73.07	$73.05	$73.10
Purchase #2	$151.85	12.168%	$170.3271	$170.33	$170.35	$170.30
Purchase #3	$108.61	13.790%	$123.5873	$123.59	$123.60	$123.60
Purchase #4	$94.60	5.354%	$99.6649	$99.66	$99.65	$99.70
Purchase #5	$61.92	9.375%	$67.725	$67.73	$67.75	$67.70
Purchase #6	$238.37	6.415%	$253.6614	$253.66	$253.65	$253.70
Purchase #7	$207.26	6.833%	$221.4221	$221.42	$221.40	$221.40
7 purchase totals =	$928.92		$1,009.4621	$1,009.46	$1,009.45	$1,009.50