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	$7.75	11.519%	$8.6427	$8.64	$8.65	$8.60
Purchase #2	$196.94	10.780%	$218.1701	$218.17	$218.15	$218.20
Purchase #3	$184.58	13.290%	$209.1107	$209.11	$209.10	$209.10
Purchase #4	$17.57	4.871%	$18.4258	$18.43	$18.45	$18.40
Purchase #5	$155.97	10.600%	$172.5028	$172.50	$172.50	$172.50
Purchase #6	$80.49	6.766%	$85.936	$85.94	$85.95	$85.90
Purchase #7	$196.63	13.205%	$222.595	$222.60	$222.60	$222.60
7 purchase totals =	$839.93		$935.3831	$935.39	$935.40	$935.30