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	$173.43	6.850%	$185.31	$185.31	$185.30	$185.30
Purchase #2	$205.33	7.652%	$221.0419	$221.04	$221.05	$221.00
Purchase #3	$185.95	10.561%	$205.5882	$205.59	$205.60	$205.60
Purchase #4	$52.44	9.610%	$57.4795	$57.48	$57.50	$57.50
Purchase #5	$114.80	12.505%	$129.1557	$129.16	$129.15	$129.20
Purchase #6	$70.92	9.375%	$77.5688	$77.57	$77.55	$77.60
Purchase #7	$172.62	9.155%	$188.4234	$188.42	$188.40	$188.40
7 purchase totals =	$975.49		$1,064.5675	$1,064.57	$1,064.55	$1,064.60