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	$114.83	5.171%	$120.7679	$120.77	$120.75	$120.80
Purchase #2	$55.96	6.374%	$59.5269	$59.53	$59.55	$59.50
Purchase #3	$242.84	8.750%	$264.0885	$264.09	$264.10	$264.10
Purchase #4	$12.85	12.583%	$14.4669	$14.47	$14.45	$14.50
Purchase #5	$135.61	3.438%	$140.2723	$140.27	$140.25	$140.30
Purchase #6	$41.60	13.178%	$47.082	$47.08	$47.10	$47.10
Purchase #7	$32.86	4.168%	$34.2296	$34.23	$34.25	$34.20
7 purchase totals =	$636.55		$680.4341	$680.44	$680.45	$680.50