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	$85.68	6.116%	$90.9202	$90.92	$90.90	$90.90
Purchase #2	$40.66	4.191%	$42.3641	$42.36	$42.35	$42.40
Purchase #3	$173.26	10.331%	$191.1595	$191.16	$191.15	$191.20
Purchase #4	$54.86	5.506%	$57.8806	$57.88	$57.90	$57.90
Purchase #5	$31.42	12.858%	$35.46	$35.46	$35.45	$35.50
Purchase #6	$175.44	7.389%	$188.4033	$188.40	$188.40	$188.40
Purchase #7	$119.47	5.843%	$126.4506	$126.45	$126.45	$126.50
7 purchase totals =	$680.79		$732.6383	$732.63	$732.60	$732.80