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	$160.58	6.824%	$171.538	$171.54	$171.55	$171.50
Purchase #2	$200.89	7.183%	$215.3199	$215.32	$215.30	$215.30
Purchase #3	$64.34	4.212%	$67.05	$67.05	$67.05	$67.10
Purchase #4	$128.30	13.763%	$145.9579	$145.96	$145.95	$146.00
Purchase #5	$11.51	3.316%	$11.8917	$11.89	$11.90	$11.90
Purchase #6	$35.42	13.662%	$40.2591	$40.26	$40.25	$40.30
Purchase #7	$148.89	5.645%	$157.2948	$157.29	$157.30	$157.30
7 purchase totals =	$749.93		$809.3114	$809.31	$809.30	$809.40