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	$89.30	12.832%	$100.759	$100.76	$100.75	$100.80
Purchase #2	$36.42	5.871%	$38.5582	$38.56	$38.55	$38.60
Purchase #3	$77.68	7.748%	$83.6986	$83.70	$83.70	$83.70
Purchase #4	$12.29	8.278%	$13.3074	$13.31	$13.30	$13.30
Purchase #5	$58.29	11.772%	$65.1519	$65.15	$65.15	$65.20
Purchase #6	$164.72	11.668%	$183.9395	$183.94	$183.95	$183.90
Purchase #7	$22.59	9.590%	$24.7564	$24.76	$24.75	$24.80
7 purchase totals =	$461.29		$510.1710	$510.18	$510.15	$510.30