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	$250.90	3.357%	$259.3227	$259.32	$259.30	$259.30
Purchase #2	$124.41	6.800%	$132.8699	$132.87	$132.85	$132.90
Purchase #3	$47.67	4.433%	$49.7832	$49.78	$49.80	$49.80
Purchase #4	$134.97	6.197%	$143.3341	$143.33	$143.35	$143.30
Purchase #5	$169.31	13.325%	$191.8706	$191.87	$191.85	$191.90
Purchase #6	$151.31	11.564%	$168.8075	$168.81	$168.80	$168.80
Purchase #7	$92.82	5.658%	$98.0718	$98.07	$98.05	$98.10
7 purchase totals =	$971.39		$1,044.0598	$1,044.05	$1,044.00	$1,044.10