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	$31.51	4.771%	$33.0133	$33.01	$33.00	$33.00
Purchase #2	$25.30	13.718%	$28.7707	$28.77	$28.75	$28.80
Purchase #3	$44.77	3.126%	$46.1695	$46.17	$46.15	$46.20
Purchase #4	$167.86	13.746%	$190.934	$190.93	$190.95	$190.90
Purchase #5	$92.94	9.232%	$101.5202	$101.52	$101.50	$101.50
Purchase #6	$75.35	4.735%	$78.9178	$78.92	$78.90	$78.90
Purchase #7	$206.41	5.863%	$218.5118	$218.51	$218.50	$218.50
7 purchase totals =	$644.14		$697.8373	$697.83	$697.75	$697.80