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	$59.28	3.370%	$61.2777	$61.28	$61.30	$61.30
Purchase #2	$96.81	7.337%	$103.9129	$103.91	$103.90	$103.90
Purchase #3	$150.45	12.530%	$169.3014	$169.30	$169.30	$169.30
Purchase #4	$108.81	9.504%	$119.1513	$119.15	$119.15	$119.20
Purchase #5	$195.91	10.381%	$216.2474	$216.25	$216.25	$216.20
Purchase #6	$48.41	12.423%	$54.424	$54.42	$54.40	$54.40
Purchase #7	$137.76	6.108%	$146.1744	$146.17	$146.15	$146.20
7 purchase totals =	$797.43		$870.4891	$870.48	$870.45	$870.50