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	$38.35	6.597%	$40.8799	$40.88	$40.90	$40.90
Purchase #2	$167.51	4.538%	$175.1116	$175.11	$175.10	$175.10
Purchase #3	$31.92	6.504%	$33.9961	$34.00	$34.00	$34.00
Purchase #4	$34.38	9.585%	$37.6753	$37.68	$37.70	$37.70
Purchase #5	$234.98	4.411%	$245.345	$245.35	$245.35	$245.30
Purchase #6	$216.43	7.197%	$232.0065	$232.01	$232.00	$232.00
Purchase #7	$19.32	13.181%	$21.8666	$21.87	$21.85	$21.90
7 purchase totals =	$742.89		$786.8810	$786.90	$786.90	$786.90