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	$20.88	11.472%	$23.2754	$23.28	$23.30	$23.30
Purchase #2	$221.71	3.862%	$230.2724	$230.27	$230.25	$230.30
Purchase #3	$239.72	12.634%	$270.0062	$270.01	$270.00	$270.00
Purchase #4	$32.94	4.103%	$34.2915	$34.29	$34.30	$34.30
Purchase #5	$124.73	13.294%	$141.3116	$141.31	$141.30	$141.30
Purchase #6	$240.83	3.764%	$249.8948	$249.89	$249.90	$249.90
Purchase #7	$162.50	12.257%	$182.4176	$182.42	$182.40	$182.40
7 purchase totals =	$1,043.31		$1,131.4695	$1,131.47	$1,131.45	$1,131.50