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	$164.45	9.692%	$180.3885	$180.39	$180.40	$180.40
Purchase #2	$196.28	10.463%	$216.8168	$216.82	$216.80	$216.80
Purchase #3	$78.27	9.300%	$85.5491	$85.55	$85.55	$85.50
Purchase #4	$152.83	4.831%	$160.2132	$160.21	$160.20	$160.20
Purchase #5	$172.80	11.128%	$192.0292	$192.03	$192.05	$192.00
Purchase #6	$96.99	3.744%	$100.6213	$100.62	$100.60	$100.60
Purchase #7	$200.43	4.201%	$208.8501	$208.85	$208.85	$208.90
7 purchase totals =	$1,062.05		$1,144.4682	$1,144.47	$1,144.45	$1,144.40