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	$37.52	5.869%	$39.722	$39.72	$39.70	$39.70
Purchase #2	$56.91	6.644%	$60.6911	$60.69	$60.70	$60.70
Purchase #3	$220.87	6.579%	$235.401	$235.40	$235.40	$235.40
Purchase #4	$205.75	11.128%	$228.6459	$228.65	$228.65	$228.60
Purchase #5	$228.78	5.714%	$241.8525	$241.85	$241.85	$241.90
Purchase #6	$86.56	13.799%	$98.5044	$98.50	$98.50	$98.50
Purchase #7	$72.50	13.613%	$82.3694	$82.37	$82.35	$82.40
7 purchase totals =	$908.89		$987.1863	$987.18	$987.15	$987.20