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	$137.64	8.780%	$149.7248	$149.72	$149.70	$149.70
Purchase #2	$47.74	7.159%	$51.1577	$51.16	$51.15	$51.20
Purchase #3	$35.82	3.402%	$37.0386	$37.04	$37.05	$37.00
Purchase #4	$147.63	3.272%	$152.4605	$152.46	$152.45	$152.50
Purchase #5	$12.70	12.127%	$14.2401	$14.24	$14.25	$14.20
Purchase #6	$96.54	6.495%	$102.8103	$102.81	$102.80	$102.80
Purchase #7	$121.89	8.680%	$132.4701	$132.47	$132.45	$132.50
7 purchase totals =	$599.96		$639.9021	$639.90	$639.85	$639.90