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	$87.65	4.530%	$91.6205	$91.62	$91.60	$91.60
Purchase #2	$150.96	13.622%	$171.5238	$171.52	$171.50	$171.50
Purchase #3	$163.27	7.224%	$175.0646	$175.06	$175.05	$175.10
Purchase #4	$49.63	11.660%	$55.4169	$55.42	$55.40	$55.40
Purchase #5	$68.59	6.704%	$73.1883	$73.19	$73.20	$73.20
Purchase #6	$37.43	7.788%	$40.345	$40.35	$40.35	$40.30
Purchase #7	$31.44	6.408%	$33.4547	$33.45	$33.45	$33.50
7 purchase totals =	$588.97		$640.6138	$640.61	$640.55	$640.60