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	$121.83	4.605%	$127.4403	$127.44	$127.45	$127.40
Purchase #2	$29.61	10.359%	$32.6773	$32.68	$32.70	$32.70
Purchase #3	$97.39	13.309%	$110.3516	$110.35	$110.35	$110.40
Purchase #4	$132.74	8.399%	$143.8888	$143.89	$143.90	$143.90
Purchase #5	$56.35	9.766%	$61.8531	$61.85	$61.85	$61.90
Purchase #6	$131.53	6.711%	$140.357	$140.36	$140.35	$140.40
Purchase #7	$240.99	10.341%	$265.9108	$265.91	$265.90	$265.90
7 purchase totals =	$810.44		$882.4789	$882.48	$882.50	$882.60