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	$112.76	4.541%	$117.8804	$117.88	$117.90	$117.90
Purchase #2	$156.31	10.768%	$173.1415	$173.14	$173.15	$173.10
Purchase #3	$181.60	13.594%	$206.2867	$206.29	$206.30	$206.30
Purchase #4	$56.80	7.204%	$60.8919	$60.89	$60.90	$60.90
Purchase #5	$27.45	6.285%	$29.1752	$29.18	$29.20	$29.20
Purchase #6	$89.31	11.301%	$99.4029	$99.40	$99.40	$99.40
Purchase #7	$99.36	6.561%	$105.879	$105.88	$105.90	$105.90
7 purchase totals =	$723.59		$792.6576	$792.66	$792.75	$792.70