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	$74.74	7.752%	$80.5338	$80.53	$80.55	$80.50
Purchase #2	$104.25	6.797%	$111.3359	$111.34	$111.35	$111.30
Purchase #3	$192.44	4.168%	$200.4609	$200.46	$200.45	$200.50
Purchase #4	$144.84	5.316%	$152.5397	$152.54	$152.55	$152.50
Purchase #5	$117.77	5.160%	$123.8469	$123.85	$123.85	$123.80
Purchase #6	$9.30	8.649%	$10.1044	$10.10	$10.10	$10.10
Purchase #7	$60.79	12.369%	$68.3091	$68.31	$68.30	$68.30
7 purchase totals =	$704.13		$747.1307	$747.13	$747.15	$747.00