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	$122.79	4.172%	$127.9128	$127.91	$127.90	$127.90
Purchase #2	$167.44	3.156%	$172.7244	$172.72	$172.70	$172.70
Purchase #3	$113.73	11.850%	$127.207	$127.21	$127.20	$127.20
Purchase #4	$66.49	8.104%	$71.8783	$71.88	$71.90	$71.90
Purchase #5	$149.47	12.728%	$168.4945	$168.49	$168.50	$168.50
Purchase #6	$184.58	9.212%	$201.5835	$201.58	$201.60	$201.60
Purchase #7	$236.49	7.202%	$253.522	$253.52	$253.50	$253.50
7 purchase totals =	$1,040.99		$1,123.3225	$1,123.31	$1,123.30	$1,123.30