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	$73.38	6.747%	$78.3309	$78.33	$78.35	$78.30
Purchase #2	$158.33	7.756%	$170.6101	$170.61	$170.60	$170.60
Purchase #3	$234.90	9.431%	$257.0534	$257.05	$257.05	$257.10
Purchase #4	$244.70	4.517%	$255.7531	$255.75	$255.75	$255.80
Purchase #5	$148.78	5.177%	$156.4823	$156.48	$156.50	$156.50
Purchase #6	$30.48	10.394%	$33.6481	$33.65	$33.65	$33.60
Purchase #7	$140.56	3.869%	$145.9983	$146.00	$146.00	$146.00
7 purchase totals =	$1,031.13		$1,097.8762	$1,097.87	$1,097.90	$1,097.90