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	$45.41	13.439%	$51.5126	$51.51	$51.50	$51.50
Purchase #2	$161.90	11.545%	$180.5914	$180.59	$180.60	$180.60
Purchase #3	$157.57	7.555%	$169.4744	$169.47	$169.45	$169.50
Purchase #4	$51.62	5.480%	$54.4488	$54.45	$54.45	$54.40
Purchase #5	$58.53	12.621%	$65.9171	$65.92	$65.90	$65.90
Purchase #6	$182.48	9.633%	$200.0583	$200.06	$200.05	$200.10
Purchase #7	$181.92	3.356%	$188.0252	$188.03	$188.05	$188.00
7 purchase totals =	$839.43		$910.0278	$910.03	$910.00	$910.00