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	$176.95	12.700%	$199.4227	$199.42	$199.40	$199.40
Purchase #2	$154.56	3.857%	$160.5214	$160.52	$160.50	$160.50
Purchase #3	$85.92	3.326%	$88.7777	$88.78	$88.80	$88.80
Purchase #4	$155.28	6.261%	$165.0021	$165.00	$165.00	$165.00
Purchase #5	$78.73	9.830%	$86.4692	$86.47	$86.45	$86.50
Purchase #6	$23.81	5.589%	$25.1407	$25.14	$25.15	$25.10
Purchase #7	$40.32	13.708%	$45.8471	$45.85	$45.85	$45.80
7 purchase totals =	$715.57		$771.1809	$771.18	$771.15	$771.10