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	$234.84	12.106%	$263.2697	$263.27	$263.25	$263.30
Purchase #2	$40.41	4.500%	$42.2285	$42.23	$42.25	$42.20
Purchase #3	$94.39	11.533%	$105.276	$105.28	$105.30	$105.30
Purchase #4	$14.33	9.470%	$15.6871	$15.69	$15.70	$15.70
Purchase #5	$205.62	11.668%	$229.6117	$229.61	$229.60	$229.60
Purchase #6	$213.33	11.596%	$238.0677	$238.07	$238.05	$238.10
Purchase #7	$227.29	6.802%	$242.7503	$242.75	$242.75	$242.80
7 purchase totals =	$1,030.21		$1,136.8910	$1,136.90	$1,136.90	$1,137.00