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	$19.49	5.389%	$20.5403	$20.54	$20.55	$20.50
Purchase #2	$224.68	11.668%	$250.8957	$250.90	$250.90	$250.90
Purchase #3	$237.70	3.616%	$246.2952	$246.30	$246.30	$246.30
Purchase #4	$141.68	6.733%	$151.2193	$151.22	$151.20	$151.20
Purchase #5	$96.61	4.366%	$100.828	$100.83	$100.85	$100.80
Purchase #6	$124.68	11.721%	$139.2937	$139.29	$139.30	$139.30
Purchase #7	$135.98	5.616%	$143.6166	$143.62	$143.60	$143.60
7 purchase totals =	$980.82		$1,052.6888	$1,052.70	$1,052.70	$1,052.60