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	$19.27	4.803%	$20.1955	$20.20	$20.20	$20.20
Purchase #2	$247.67	6.643%	$264.1227	$264.12	$264.10	$264.10
Purchase #3	$13.66	6.153%	$14.5005	$14.50	$14.50	$14.50
Purchase #4	$92.77	4.401%	$96.8528	$96.85	$96.85	$96.90
Purchase #5	$140.67	12.227%	$157.8697	$157.87	$157.85	$157.90
Purchase #6	$209.72	10.289%	$231.2981	$231.30	$231.30	$231.30
Purchase #7	$205.85	5.820%	$217.8305	$217.83	$217.85	$217.80
7 purchase totals =	$929.61		$1,002.6698	$1,002.67	$1,002.65	$1,002.70