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	$185.27	3.295%	$191.3746	$191.37	$191.35	$191.40
Purchase #2	$95.91	9.849%	$105.3562	$105.36	$105.35	$105.40
Purchase #3	$229.85	11.661%	$256.6528	$256.65	$256.65	$256.70
Purchase #4	$43.73	13.591%	$49.6733	$49.67	$49.65	$49.70
Purchase #5	$42.67	5.486%	$45.0109	$45.01	$45.00	$45.00
Purchase #6	$224.72	10.724%	$248.819	$248.82	$248.80	$248.80
Purchase #7	$127.82	12.155%	$143.3565	$143.36	$143.35	$143.40
7 purchase totals =	$949.97		$1,040.2433	$1,040.24	$1,040.15	$1,040.40