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	$134.62	8.835%	$146.5137	$146.51	$146.50	$146.50
Purchase #2	$29.90	9.874%	$32.8523	$32.85	$32.85	$32.90
Purchase #3	$57.33	13.779%	$65.2295	$65.23	$65.25	$65.20
Purchase #4	$202.94	9.644%	$222.5115	$222.51	$222.50	$222.50
Purchase #5	$222.75	12.595%	$250.8054	$250.81	$250.80	$250.80
Purchase #6	$18.80	4.486%	$19.6434	$19.64	$19.65	$19.60
Purchase #7	$160.70	7.843%	$173.3037	$173.30	$173.30	$173.30
7 purchase totals =	$827.04		$910.8595	$910.85	$910.85	$910.80