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	$29.50	11.375%	$32.8556	$32.86	$32.85	$32.90
Purchase #2	$70.81	13.513%	$80.3786	$80.38	$80.40	$80.40
Purchase #3	$160.50	6.682%	$171.2246	$171.22	$171.20	$171.20
Purchase #4	$24.80	10.831%	$27.4861	$27.49	$27.50	$27.50
Purchase #5	$26.40	4.466%	$27.579	$27.58	$27.60	$27.60
Purchase #6	$110.42	6.390%	$117.4758	$117.48	$117.50	$117.50
Purchase #7	$41.83	5.421%	$44.0976	$44.10	$44.10	$44.10
7 purchase totals =	$464.26		$501.0973	$501.11	$501.15	$501.20