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	$148.41	13.744%	$168.8075	$168.81	$168.80	$168.80
Purchase #2	$82.97	4.734%	$86.8978	$86.90	$86.90	$86.90
Purchase #3	$50.26	10.381%	$55.4775	$55.48	$55.50	$55.50
Purchase #4	$25.69	7.103%	$27.5148	$27.51	$27.50	$27.50
Purchase #5	$221.50	11.746%	$247.5174	$247.52	$247.50	$247.50
Purchase #6	$18.74	3.388%	$19.3749	$19.37	$19.35	$19.40
Purchase #7	$12.88	4.106%	$13.4089	$13.41	$13.40	$13.40
7 purchase totals =	$560.45		$618.9988	$619.00	$618.95	$619.00