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	$98.80	12.530%	$111.1796	$111.18	$111.20	$111.20
Purchase #2	$71.61	12.251%	$80.3829	$80.38	$80.40	$80.40
Purchase #3	$64.87	11.521%	$72.3437	$72.34	$72.35	$72.30
Purchase #4	$87.91	5.514%	$92.7574	$92.76	$92.75	$92.80
Purchase #5	$244.39	12.352%	$274.5771	$274.58	$274.60	$274.60
Purchase #6	$235.52	3.812%	$244.498	$244.50	$244.50	$244.50
Purchase #7	$133.49	4.479%	$139.469	$139.47	$139.45	$139.50
7 purchase totals =	$936.59		$1,015.2077	$1,015.21	$1,015.25	$1,015.30