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	$85.99	11.810%	$96.1454	$96.15	$96.15	$96.10
Purchase #2	$39.49	3.347%	$40.8117	$40.81	$40.80	$40.80
Purchase #3	$231.60	6.793%	$247.3326	$247.33	$247.35	$247.30
Purchase #4	$61.57	12.760%	$69.4263	$69.43	$69.45	$69.40
Purchase #5	$83.72	5.639%	$88.441	$88.44	$88.45	$88.40
Purchase #6	$20.61	4.211%	$21.4779	$21.48	$21.50	$21.50
Purchase #7	$24.33	11.518%	$27.1323	$27.13	$27.15	$27.10
7 purchase totals =	$547.31		$590.7672	$590.77	$590.85	$590.60