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	$49.90	5.659%	$52.7238	$52.72	$52.70	$52.70
Purchase #2	$187.53	11.848%	$209.7486	$209.75	$209.75	$209.70
Purchase #3	$84.56	4.345%	$88.2341	$88.23	$88.25	$88.20
Purchase #4	$249.66	9.689%	$273.8496	$273.85	$273.85	$273.80
Purchase #5	$99.92	3.593%	$103.5101	$103.51	$103.50	$103.50
Purchase #6	$103.73	7.821%	$111.8427	$111.84	$111.85	$111.80
Purchase #7	$125.37	3.208%	$129.3919	$129.39	$129.40	$129.40
7 purchase totals =	$900.67		$969.3008	$969.29	$969.30	$969.10