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	$154.96	9.723%	$170.0268	$170.03	$170.05	$170.00
Purchase #2	$93.54	6.670%	$99.7791	$99.78	$99.80	$99.80
Purchase #3	$81.95	8.328%	$88.7748	$88.77	$88.75	$88.80
Purchase #4	$239.69	13.691%	$272.506	$272.51	$272.50	$272.50
Purchase #5	$31.31	6.643%	$33.3899	$33.39	$33.40	$33.40
Purchase #6	$68.53	11.606%	$76.4836	$76.48	$76.50	$76.50
Purchase #7	$135.33	4.419%	$141.3102	$141.31	$141.30	$141.30
7 purchase totals =	$805.31		$882.2704	$882.27	$882.30	$882.30