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	$206.58	5.688%	$218.3303	$218.33	$218.35	$218.30
Purchase #2	$56.70	4.874%	$59.4636	$59.46	$59.45	$59.50
Purchase #3	$241.69	6.778%	$258.0717	$258.07	$258.05	$258.10
Purchase #4	$91.54	8.111%	$98.9648	$98.96	$98.95	$99.00
Purchase #5	$50.27	11.288%	$55.9445	$55.94	$55.95	$55.90
Purchase #6	$91.59	7.395%	$98.3631	$98.36	$98.35	$98.40
Purchase #7	$66.79	10.456%	$73.7736	$73.77	$73.75	$73.80
7 purchase totals =	$805.16		$862.9116	$862.89	$862.85	$863.00