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	$161.43	7.867%	$174.1297	$174.13	$174.15	$174.10
Purchase #2	$70.83	10.446%	$78.2289	$78.23	$78.25	$78.20
Purchase #3	$184.29	12.824%	$207.9233	$207.92	$207.90	$207.90
Purchase #4	$37.82	11.160%	$42.0407	$42.04	$42.05	$42.00
Purchase #5	$218.28	5.198%	$229.6262	$229.63	$229.65	$229.60
Purchase #6	$82.96	8.752%	$90.2207	$90.22	$90.20	$90.20
Purchase #7	$159.38	4.749%	$166.949	$166.95	$166.95	$166.90
7 purchase totals =	$914.99		$989.1185	$989.12	$989.15	$988.90