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	$138.38	10.140%	$152.4117	$152.41	$152.40	$152.40
Purchase #2	$185.86	11.639%	$207.4922	$207.49	$207.50	$207.50
Purchase #3	$162.36	11.782%	$181.4893	$181.49	$181.50	$181.50
Purchase #4	$31.42	4.557%	$32.8518	$32.85	$32.85	$32.90
Purchase #5	$30.47	12.421%	$34.2547	$34.25	$34.25	$34.30
Purchase #6	$38.42	11.517%	$42.8448	$42.84	$42.85	$42.80
Purchase #7	$167.62	13.569%	$190.3644	$190.36	$190.35	$190.40
7 purchase totals =	$754.53		$841.7089	$841.69	$841.70	$841.80