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	$33.80	6.218%	$35.9017	$35.90	$35.90	$35.90
Purchase #2	$170.94	4.309%	$178.3058	$178.31	$178.30	$178.30
Purchase #3	$32.35	10.356%	$35.7002	$35.70	$35.70	$35.70
Purchase #4	$36.66	7.831%	$39.5308	$39.53	$39.55	$39.50
Purchase #5	$207.39	11.356%	$230.9412	$230.94	$230.95	$230.90
Purchase #6	$39.56	7.783%	$42.639	$42.64	$42.65	$42.60
Purchase #7	$250.91	8.195%	$271.4721	$271.47	$271.45	$271.50
7 purchase totals =	$771.61		$834.4908	$834.49	$834.50	$834.40