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	$160.85	11.476%	$179.3091	$179.31	$179.30	$179.30
Purchase #2	$82.56	8.749%	$89.7832	$89.78	$89.80	$89.80
Purchase #3	$77.73	12.209%	$87.2201	$87.22	$87.20	$87.20
Purchase #4	$204.37	4.476%	$213.5176	$213.52	$213.50	$213.50
Purchase #5	$80.51	11.605%	$89.8532	$89.85	$89.85	$89.90
Purchase #6	$32.97	6.517%	$35.1187	$35.12	$35.10	$35.10
Purchase #7	$149.28	7.782%	$160.897	$160.90	$160.90	$160.90
7 purchase totals =	$788.27		$855.6989	$855.70	$855.65	$855.70