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	$166.30	8.120%	$179.8036	$179.80	$179.80	$179.80
Purchase #2	$216.72	13.731%	$246.4778	$246.48	$246.50	$246.50
Purchase #3	$99.35	3.174%	$102.5034	$102.50	$102.50	$102.50
Purchase #4	$68.45	13.399%	$77.6216	$77.62	$77.60	$77.60
Purchase #5	$80.79	12.342%	$90.7611	$90.76	$90.75	$90.80
Purchase #6	$229.34	6.611%	$244.5017	$244.50	$244.50	$244.50
Purchase #7	$224.78	7.378%	$241.3643	$241.36	$241.35	$241.40
7 purchase totals =	$1,085.73		$1,183.0335	$1,183.02	$1,183.00	$1,183.10