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	$64.49	13.310%	$73.0736	$73.07	$73.05	$73.10
Purchase #2	$66.61	9.333%	$72.8267	$72.83	$72.85	$72.80
Purchase #3	$172.82	7.129%	$185.1403	$185.14	$185.15	$185.10
Purchase #4	$249.26	6.246%	$264.8288	$264.83	$264.85	$264.80
Purchase #5	$16.78	8.517%	$18.2092	$18.21	$18.20	$18.20
Purchase #6	$103.26	6.662%	$110.1392	$110.14	$110.15	$110.10
Purchase #7	$246.37	3.380%	$254.6973	$254.70	$254.70	$254.70
7 purchase totals =	$919.59		$978.9151	$978.92	$978.95	$978.80