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	$90.73	8.456%	$98.4021	$98.40	$98.40	$98.40
Purchase #2	$206.58	11.853%	$231.0659	$231.07	$231.05	$231.10
Purchase #3	$79.41	5.363%	$83.6688	$83.67	$83.65	$83.70
Purchase #4	$60.83	9.141%	$66.3905	$66.39	$66.40	$66.40
Purchase #5	$106.56	4.185%	$111.0195	$111.02	$111.00	$111.00
Purchase #6	$199.67	12.561%	$224.7505	$224.75	$224.75	$224.80
Purchase #7	$168.28	12.242%	$188.8808	$188.88	$188.90	$188.90
7 purchase totals =	$912.06		$1,004.1781	$1,004.18	$1,004.15	$1,004.30