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	$6.51	5.327%	$6.8568	$6.86	$6.85	$6.90
Purchase #2	$176.37	6.838%	$188.4302	$188.43	$188.45	$188.40
Purchase #3	$94.48	9.661%	$103.6077	$103.61	$103.60	$103.60
Purchase #4	$172.43	11.869%	$192.8957	$192.90	$192.90	$192.90
Purchase #5	$228.77	6.510%	$243.6629	$243.66	$243.65	$243.70
Purchase #6	$130.97	11.798%	$146.4218	$146.42	$146.40	$146.40
Purchase #7	$248.47	10.827%	$275.3718	$275.37	$275.35	$275.40
7 purchase totals =	$1,058.00		$1,157.2469	$1,157.25	$1,157.20	$1,157.30