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	$50.48	13.723%	$57.4074	$57.41	$57.40	$57.40
Purchase #2	$110.96	13.621%	$126.0739	$126.07	$126.05	$126.10
Purchase #3	$208.63	10.670%	$230.8908	$230.89	$230.90	$230.90
Purchase #4	$181.90	4.811%	$190.6512	$190.65	$190.65	$190.70
Purchase #5	$184.73	4.324%	$192.7177	$192.72	$192.70	$192.70
Purchase #6	$113.81	12.280%	$127.7859	$127.79	$127.80	$127.80
Purchase #7	$6.69	11.784%	$7.4783	$7.48	$7.50	$7.50
7 purchase totals =	$857.20		$933.0052	$933.01	$933.00	$933.10