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	$15.50	12.624%	$17.4567	$17.46	$17.45	$17.50
Purchase #2	$228.58	4.505%	$238.8775	$238.88	$238.90	$238.90
Purchase #3	$84.57	6.569%	$90.1254	$90.13	$90.15	$90.10
Purchase #4	$93.82	12.492%	$105.54	$105.54	$105.55	$105.50
Purchase #5	$237.81	8.597%	$258.2545	$258.25	$258.25	$258.30
Purchase #6	$225.61	11.165%	$250.7994	$250.80	$250.80	$250.80
Purchase #7	$175.64	6.383%	$186.8511	$186.85	$186.85	$186.90
7 purchase totals =	$1,061.53		$1,147.9046	$1,147.91	$1,147.95	$1,148.00