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	$158.56	7.394%	$170.2839	$170.28	$170.30	$170.30
Purchase #2	$71.42	10.345%	$78.8084	$78.81	$78.80	$78.80
Purchase #3	$157.79	6.855%	$168.6065	$168.61	$168.60	$168.60
Purchase #4	$187.31	12.439%	$210.6095	$210.61	$210.60	$210.60
Purchase #5	$234.67	9.254%	$256.3864	$256.39	$256.40	$256.40
Purchase #6	$40.81	3.189%	$42.1114	$42.11	$42.10	$42.10
Purchase #7	$65.91	4.582%	$68.93	$68.93	$68.95	$68.90
7 purchase totals =	$916.47		$995.7361	$995.74	$995.75	$995.70