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	$180.42	6.230%	$191.6602	$191.66	$191.65	$191.70
Purchase #2	$99.39	12.138%	$111.454	$111.45	$111.45	$111.50
Purchase #3	$73.69	13.150%	$83.3802	$83.38	$83.40	$83.40
Purchase #4	$213.31	11.736%	$238.3441	$238.34	$238.35	$238.30
Purchase #5	$140.74	5.478%	$148.4497	$148.45	$148.45	$148.40
Purchase #6	$226.50	3.140%	$233.6121	$233.61	$233.60	$233.60
Purchase #7	$71.73	13.450%	$81.3777	$81.38	$81.40	$81.40
7 purchase totals =	$1,005.78		$1,088.2780	$1,088.27	$1,088.30	$1,088.30