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	$133.28	12.643%	$150.1306	$150.13	$150.15	$150.10
Purchase #2	$70.65	8.805%	$76.8707	$76.87	$76.85	$76.90
Purchase #3	$226.89	12.453%	$255.1446	$255.14	$255.15	$255.10
Purchase #4	$165.40	6.176%	$175.6151	$175.62	$175.60	$175.60
Purchase #5	$229.64	3.313%	$237.248	$237.25	$237.25	$237.20
Purchase #6	$21.41	13.186%	$24.2331	$24.23	$24.25	$24.20
Purchase #7	$215.35	3.488%	$222.8614	$222.86	$222.85	$222.90
7 purchase totals =	$1,062.62		$1,142.1035	$1,142.10	$1,142.10	$1,142.00