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	$145.53	3.598%	$150.7662	$150.77	$150.75	$150.80
Purchase #2	$6.85	6.799%	$7.3157	$7.32	$7.30	$7.30
Purchase #3	$107.71	8.314%	$116.665	$116.67	$116.65	$116.70
Purchase #4	$33.59	12.766%	$37.8781	$37.88	$37.90	$37.90
Purchase #5	$45.42	13.609%	$51.6012	$51.60	$51.60	$51.60
Purchase #6	$142.71	8.352%	$154.6291	$154.63	$154.65	$154.60
Purchase #7	$56.48	6.830%	$60.3376	$60.34	$60.35	$60.30
7 purchase totals =	$538.29		$579.1929	$579.21	$579.20	$579.20