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	$52.28	6.202%	$55.5224	$55.52	$55.50	$55.50
Purchase #2	$173.68	5.308%	$182.8989	$182.90	$182.90	$182.90
Purchase #3	$209.75	10.137%	$231.0124	$231.01	$231.00	$231.00
Purchase #4	$90.32	11.748%	$100.9308	$100.93	$100.95	$100.90
Purchase #5	$161.82	10.813%	$179.3176	$179.32	$179.30	$179.30
Purchase #6	$183.72	3.620%	$190.3707	$190.37	$190.35	$190.40
Purchase #7	$70.46	13.800%	$80.1835	$80.18	$80.20	$80.20
7 purchase totals =	$942.03		$1,020.2363	$1,020.23	$1,020.20	$1,020.20