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	$156.40	5.554%	$165.0865	$165.09	$165.10	$165.10
Purchase #2	$66.60	7.175%	$71.3786	$71.38	$71.40	$71.40
Purchase #3	$91.50	4.387%	$95.5141	$95.51	$95.50	$95.50
Purchase #4	$94.96	13.631%	$107.904	$107.90	$107.90	$107.90
Purchase #5	$76.28	9.505%	$83.5304	$83.53	$83.55	$83.50
Purchase #6	$242.61	6.446%	$258.2486	$258.25	$258.25	$258.20
Purchase #7	$178.57	9.141%	$194.8931	$194.89	$194.90	$194.90
7 purchase totals =	$906.92		$976.5553	$976.55	$976.60	$976.50