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	$30.90	6.318%	$32.8523	$32.85	$32.85	$32.90
Purchase #2	$81.60	5.785%	$86.3206	$86.32	$86.30	$86.30
Purchase #3	$9.72	5.857%	$10.2893	$10.29	$10.30	$10.30
Purchase #4	$250.46	5.108%	$263.2535	$263.25	$263.25	$263.30
Purchase #5	$120.36	10.377%	$132.8498	$132.85	$132.85	$132.80
Purchase #6	$35.38	7.691%	$38.1011	$38.10	$38.10	$38.10
Purchase #7	$91.90	8.652%	$99.8512	$99.85	$99.85	$99.90
7 purchase totals =	$620.32		$663.5178	$663.51	$663.50	$663.60