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	$136.41	3.675%	$141.4231	$141.42	$141.40	$141.40
Purchase #2	$59.90	5.146%	$62.9825	$62.98	$63.00	$63.00
Purchase #3	$89.34	12.814%	$100.788	$100.79	$100.80	$100.80
Purchase #4	$151.45	4.387%	$158.0941	$158.09	$158.10	$158.10
Purchase #5	$203.98	6.539%	$217.3183	$217.32	$217.30	$217.30
Purchase #6	$6.64	5.828%	$7.027	$7.03	$7.05	$7.00
Purchase #7	$29.90	10.297%	$32.9788	$32.98	$33.00	$33.00
7 purchase totals =	$677.62		$720.6118	$720.61	$720.65	$720.60