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	$88.53	13.384%	$100.3789	$100.38	$100.40	$100.40
Purchase #2	$122.25	12.284%	$137.2672	$137.27	$137.25	$137.30
Purchase #3	$26.37	6.797%	$28.1624	$28.16	$28.15	$28.20
Purchase #4	$231.37	4.495%	$241.7701	$241.77	$241.75	$241.80
Purchase #5	$69.55	11.655%	$77.6561	$77.66	$77.65	$77.70
Purchase #6	$52.54	3.761%	$54.516	$54.52	$54.50	$54.50
Purchase #7	$13.73	3.755%	$14.2456	$14.25	$14.25	$14.20
7 purchase totals =	$604.34		$653.9963	$654.01	$653.95	$654.10