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	$21.40	4.324%	$22.3253	$22.33	$22.35	$22.30
Purchase #2	$55.56	10.597%	$61.4477	$61.45	$61.45	$61.40
Purchase #3	$74.65	4.867%	$78.2832	$78.28	$78.30	$78.30
Purchase #4	$11.32	11.300%	$12.5992	$12.60	$12.60	$12.60
Purchase #5	$187.49	12.310%	$210.57	$210.57	$210.55	$210.60
Purchase #6	$250.86	5.662%	$265.0637	$265.06	$265.05	$265.10
Purchase #7	$18.34	13.576%	$20.8298	$20.83	$20.85	$20.80
7 purchase totals =	$619.62		$671.1189	$671.12	$671.15	$671.10