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	$37.63	7.687%	$40.5226	$40.52	$40.50	$40.50
Purchase #2	$243.41	4.409%	$254.1419	$254.14	$254.15	$254.10
Purchase #3	$194.65	8.415%	$211.0298	$211.03	$211.05	$211.00
Purchase #4	$87.39	12.711%	$98.4981	$98.50	$98.50	$98.50
Purchase #5	$59.57	13.725%	$67.746	$67.75	$67.75	$67.70
Purchase #6	$65.57	12.261%	$73.6095	$73.61	$73.60	$73.60
Purchase #7	$76.40	13.243%	$86.5177	$86.52	$86.50	$86.50
7 purchase totals =	$764.62		$832.0656	$832.07	$832.05	$831.90