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	$120.34	5.335%	$126.7601	$126.76	$126.75	$126.80
Purchase #2	$156.47	10.496%	$172.8931	$172.89	$172.90	$172.90
Purchase #3	$235.72	3.524%	$244.0268	$244.03	$244.05	$244.00
Purchase #4	$98.88	6.792%	$105.5959	$105.60	$105.60	$105.60
Purchase #5	$220.30	11.432%	$245.4847	$245.48	$245.50	$245.50
Purchase #6	$51.43	6.545%	$54.7961	$54.80	$54.80	$54.80
Purchase #7	$115.95	6.252%	$123.1992	$123.20	$123.20	$123.20
7 purchase totals =	$999.09		$1,072.7559	$1,072.76	$1,072.80	$1,072.80