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	$191.46	6.667%	$204.2246	$204.22	$204.20	$204.20
Purchase #2	$78.91	5.599%	$83.3282	$83.33	$83.35	$83.30
Purchase #3	$44.69	12.680%	$50.3567	$50.36	$50.35	$50.40
Purchase #4	$107.69	12.528%	$121.1814	$121.18	$121.20	$121.20
Purchase #5	$33.55	12.141%	$37.6233	$37.62	$37.60	$37.60
Purchase #6	$143.86	11.308%	$160.1277	$160.13	$160.15	$160.10
Purchase #7	$160.25	5.142%	$168.4901	$168.49	$168.50	$168.50
7 purchase totals =	$760.41		$825.3320	$825.33	$825.35	$825.30