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	$57.81	11.816%	$64.6408	$64.64	$64.65	$64.60
Purchase #2	$54.39	11.193%	$60.4779	$60.48	$60.50	$60.50
Purchase #3	$128.38	13.175%	$145.2941	$145.29	$145.30	$145.30
Purchase #4	$205.73	10.603%	$227.5436	$227.54	$227.55	$227.50
Purchase #5	$248.61	6.671%	$265.1948	$265.19	$265.20	$265.20
Purchase #6	$197.34	10.350%	$217.7647	$217.76	$217.75	$217.80
Purchase #7	$127.86	11.194%	$142.1726	$142.17	$142.15	$142.20
7 purchase totals =	$1,020.12		$1,123.0885	$1,123.07	$1,123.10	$1,123.10