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	$91.53	9.721%	$100.4276	$100.43	$100.45	$100.40
Purchase #2	$9.40	13.750%	$10.6925	$10.69	$10.70	$10.70
Purchase #3	$105.31	3.655%	$109.1591	$109.16	$109.15	$109.20
Purchase #4	$190.70	11.738%	$213.0844	$213.08	$213.10	$213.10
Purchase #5	$19.25	10.386%	$21.2493	$21.25	$21.25	$21.20
Purchase #6	$231.67	11.559%	$258.4487	$258.45	$258.45	$258.40
Purchase #7	$36.25	3.844%	$37.6435	$37.64	$37.65	$37.60
7 purchase totals =	$684.11		$750.7051	$750.70	$750.75	$750.60