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	$55.44	7.106%	$59.3796	$59.38	$59.40	$59.40
Purchase #2	$75.69	10.102%	$83.3362	$83.34	$83.35	$83.30
Purchase #3	$187.30	9.165%	$204.466	$204.47	$204.45	$204.50
Purchase #4	$27.81	4.198%	$28.9775	$28.98	$29.00	$29.00
Purchase #5	$130.98	10.191%	$144.3282	$144.33	$144.35	$144.30
Purchase #6	$158.48	12.703%	$178.6117	$178.61	$178.60	$178.60
Purchase #7	$59.30	10.746%	$65.6724	$65.67	$65.65	$65.70
7 purchase totals =	$695.00		$764.7716	$764.78	$764.80	$764.80