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	$127.85	11.267%	$142.2549	$142.25	$142.25	$142.30
Purchase #2	$244.76	4.390%	$255.505	$255.51	$255.50	$255.50
Purchase #3	$244.73	6.741%	$261.2272	$261.23	$261.25	$261.20
Purchase #4	$174.39	12.290%	$195.8225	$195.82	$195.80	$195.80
Purchase #5	$150.91	9.306%	$164.9537	$164.95	$164.95	$165.00
Purchase #6	$197.62	11.629%	$220.6012	$220.60	$220.60	$220.60
Purchase #7	$45.51	11.267%	$50.6376	$50.64	$50.65	$50.60
7 purchase totals =	$1,185.77		$1,291.0021	$1,291.00	$1,291.00	$1,291.00