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	$29.90	3.556%	$30.9632	$30.96	$30.95	$31.00
Purchase #2	$111.89	7.632%	$120.4294	$120.43	$120.45	$120.40
Purchase #3	$134.25	10.622%	$148.51	$148.51	$148.50	$148.50
Purchase #4	$238.93	10.247%	$263.4132	$263.41	$263.40	$263.40
Purchase #5	$102.81	5.402%	$108.3638	$108.36	$108.35	$108.40
Purchase #6	$43.87	11.361%	$48.8541	$48.85	$48.85	$48.90
Purchase #7	$101.35	10.325%	$111.8144	$111.81	$111.80	$111.80
7 purchase totals =	$763.00		$832.3481	$832.33	$832.30	$832.40