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	$98.86	6.186%	$104.9755	$104.98	$105.00	$105.00
Purchase #2	$212.78	5.855%	$225.2383	$225.24	$225.25	$225.20
Purchase #3	$17.29	4.562%	$18.0788	$18.08	$18.10	$18.10
Purchase #4	$87.38	8.436%	$94.7514	$94.75	$94.75	$94.80
Purchase #5	$7.29	3.154%	$7.5199	$7.52	$7.50	$7.50
Purchase #6	$53.51	4.301%	$55.8115	$55.81	$55.80	$55.80
Purchase #7	$127.89	12.717%	$144.1538	$144.15	$144.15	$144.20
7 purchase totals =	$605.00		$650.5292	$650.53	$650.55	$650.60