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	$36.78	7.620%	$39.5826	$39.58	$39.60	$39.60
Purchase #2	$148.94	3.700%	$154.4508	$154.45	$154.45	$154.50
Purchase #3	$64.25	11.117%	$71.3927	$71.39	$71.40	$71.40
Purchase #4	$65.84	7.713%	$70.9182	$70.92	$70.90	$70.90
Purchase #5	$38.92	9.155%	$42.4831	$42.48	$42.50	$42.50
Purchase #6	$89.50	13.544%	$101.6219	$101.62	$101.60	$101.60
Purchase #7	$107.77	9.339%	$117.8346	$117.83	$117.85	$117.80
7 purchase totals =	$552.00		$598.2839	$598.27	$598.30	$598.30