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	$82.75	8.113%	$89.4635	$89.46	$89.45	$89.50
Purchase #2	$106.89	5.412%	$112.6749	$112.67	$112.65	$112.70
Purchase #3	$73.56	11.210%	$81.8061	$81.81	$81.80	$81.80
Purchase #4	$101.61	13.103%	$114.924	$114.92	$114.90	$114.90
Purchase #5	$125.50	7.160%	$134.4858	$134.49	$134.50	$134.50
Purchase #6	$115.50	12.862%	$130.3556	$130.36	$130.35	$130.40
Purchase #7	$22.34	11.515%	$24.9125	$24.91	$24.90	$24.90
7 purchase totals =	$628.15		$688.6224	$688.62	$688.55	$688.70