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	$39.54	6.865%	$42.2544	$42.25	$42.25	$42.30
Purchase #2	$37.79	6.231%	$40.1447	$40.14	$40.15	$40.10
Purchase #3	$132.88	9.471%	$145.4651	$145.47	$145.45	$145.50
Purchase #4	$42.74	13.277%	$48.4146	$48.41	$48.40	$48.40
Purchase #5	$71.54	12.770%	$80.6757	$80.68	$80.70	$80.70
Purchase #6	$32.83	12.185%	$36.8303	$36.83	$36.85	$36.80
Purchase #7	$201.46	11.861%	$225.3552	$225.36	$225.35	$225.40
7 purchase totals =	$558.78		$619.1400	$619.14	$619.15	$619.20