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	$6.72	11.521%	$7.4942	$7.49	$7.50	$7.50
Purchase #2	$136.65	5.713%	$144.4568	$144.46	$144.45	$144.50
Purchase #3	$79.48	3.790%	$82.4923	$82.49	$82.50	$82.50
Purchase #4	$103.92	8.301%	$112.5464	$112.55	$112.55	$112.50
Purchase #5	$136.80	6.439%	$145.6086	$145.61	$145.60	$145.60
Purchase #6	$16.74	13.827%	$19.0546	$19.05	$19.05	$19.10
Purchase #7	$75.81	10.562%	$83.8171	$83.82	$83.80	$83.80
7 purchase totals =	$556.12		$595.4700	$595.47	$595.45	$595.50