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	$39.75	8.771%	$43.2365	$43.24	$43.25	$43.20
Purchase #2	$83.93	7.699%	$90.3918	$90.39	$90.40	$90.40
Purchase #3	$196.64	4.168%	$204.836	$204.84	$204.85	$204.80
Purchase #4	$6.82	13.385%	$7.7329	$7.73	$7.75	$7.70
Purchase #5	$46.66	3.865%	$48.4634	$48.46	$48.45	$48.50
Purchase #6	$168.73	12.511%	$189.8398	$189.84	$189.85	$189.80
Purchase #7	$152.50	11.618%	$170.2175	$170.22	$170.20	$170.20
7 purchase totals =	$695.03		$754.7179	$754.72	$754.75	$754.60