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	$61.54	7.727%	$66.2952	$66.30	$66.30	$66.30
Purchase #2	$239.27	7.582%	$257.4115	$257.41	$257.40	$257.40
Purchase #3	$221.86	3.441%	$229.4942	$229.49	$229.50	$229.50
Purchase #4	$170.43	5.180%	$179.2583	$179.26	$179.25	$179.30
Purchase #5	$152.72	10.551%	$168.8335	$168.83	$168.85	$168.80
Purchase #6	$250.49	11.669%	$279.7197	$279.72	$279.70	$279.70
Purchase #7	$140.73	12.518%	$158.3466	$158.35	$158.35	$158.30
7 purchase totals =	$1,237.04		$1,339.3590	$1,339.36	$1,339.35	$1,339.30