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	$102.43	6.177%	$108.7571	$108.76	$108.75	$108.80
Purchase #2	$75.72	3.348%	$78.2551	$78.26	$78.25	$78.30
Purchase #3	$137.75	9.265%	$150.5125	$150.51	$150.50	$150.50
Purchase #4	$235.71	11.678%	$263.2362	$263.24	$263.25	$263.20
Purchase #5	$97.39	6.670%	$103.8859	$103.89	$103.90	$103.90
Purchase #6	$64.83	10.767%	$71.8102	$71.81	$71.80	$71.80
Purchase #7	$137.64	4.494%	$143.8255	$143.83	$143.85	$143.80
7 purchase totals =	$851.47		$920.2825	$920.30	$920.30	$920.30