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	$249.87	6.459%	$266.0091	$266.01	$266.00	$266.00
Purchase #2	$240.89	4.208%	$251.0267	$251.03	$251.05	$251.00
Purchase #3	$182.56	13.871%	$207.8829	$207.88	$207.90	$207.90
Purchase #4	$94.43	6.673%	$100.7313	$100.73	$100.75	$100.70
Purchase #5	$99.84	5.415%	$105.2463	$105.25	$105.25	$105.20
Purchase #6	$128.93	6.718%	$137.5915	$137.59	$137.60	$137.60
Purchase #7	$216.58	11.233%	$240.9084	$240.91	$240.90	$240.90
7 purchase totals =	$1,213.10		$1,309.3962	$1,309.40	$1,309.45	$1,309.30