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	$18.55	13.846%	$21.1184	$21.12	$21.10	$21.10
Purchase #2	$201.40	9.278%	$220.0859	$220.09	$220.10	$220.10
Purchase #3	$69.65	10.414%	$76.9034	$76.90	$76.90	$76.90
Purchase #4	$95.94	10.297%	$105.8189	$105.82	$105.80	$105.80
Purchase #5	$109.33	8.678%	$118.8177	$118.82	$118.80	$118.80
Purchase #6	$83.92	11.364%	$93.4567	$93.46	$93.45	$93.50
Purchase #7	$99.33	5.840%	$105.1309	$105.13	$105.15	$105.10
7 purchase totals =	$678.12		$741.3319	$741.34	$741.30	$741.30