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	$138.34	8.408%	$149.9716	$149.97	$149.95	$150.00
Purchase #2	$194.90	9.106%	$212.6476	$212.65	$212.65	$212.60
Purchase #3	$164.70	8.855%	$179.2842	$179.28	$179.30	$179.30
Purchase #4	$162.72	13.783%	$185.1477	$185.15	$185.15	$185.10
Purchase #5	$162.54	10.185%	$179.0947	$179.09	$179.10	$179.10
Purchase #6	$138.89	3.846%	$144.2317	$144.23	$144.25	$144.20
Purchase #7	$152.33	5.350%	$160.4797	$160.48	$160.50	$160.50
7 purchase totals =	$1,114.42		$1,210.8572	$1,210.85	$1,210.90	$1,210.80