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	$125.77	13.333%	$142.5389	$142.54	$142.55	$142.50
Purchase #2	$243.87	8.722%	$265.1403	$265.14	$265.15	$265.10
Purchase #3	$18.98	13.758%	$21.5913	$21.59	$21.60	$21.60
Purchase #4	$109.41	8.803%	$119.0414	$119.04	$119.05	$119.00
Purchase #5	$36.34	10.102%	$40.0111	$40.01	$40.00	$40.00
Purchase #6	$60.60	10.199%	$66.7806	$66.78	$66.80	$66.80
Purchase #7	$36.32	6.123%	$38.5439	$38.54	$38.55	$38.50
7 purchase totals =	$631.29		$693.6475	$693.64	$693.70	$693.50