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	$168.49	6.364%	$179.2127	$179.21	$179.20	$179.20
Purchase #2	$160.74	7.701%	$173.1186	$173.12	$173.10	$173.10
Purchase #3	$76.28	9.636%	$83.6303	$83.63	$83.65	$83.60
Purchase #4	$82.59	8.873%	$89.9182	$89.92	$89.90	$89.90
Purchase #5	$35.94	3.152%	$37.0728	$37.07	$37.05	$37.10
Purchase #6	$48.98	12.436%	$55.0712	$55.07	$55.05	$55.10
Purchase #7	$187.77	13.217%	$212.5876	$212.59	$212.60	$212.60
7 purchase totals =	$760.79		$830.6114	$830.61	$830.55	$830.60