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	$130.50	6.804%	$139.3792	$139.38	$139.40	$139.40
Purchase #2	$88.67	13.152%	$100.3319	$100.33	$100.35	$100.30
Purchase #3	$42.89	4.770%	$44.9359	$44.94	$44.95	$44.90
Purchase #4	$223.55	8.345%	$242.2052	$242.21	$242.20	$242.20
Purchase #5	$50.98	7.676%	$54.8932	$54.89	$54.90	$54.90
Purchase #6	$241.78	3.810%	$250.9918	$250.99	$251.00	$251.00
Purchase #7	$120.34	6.509%	$128.1729	$128.17	$128.15	$128.20
7 purchase totals =	$898.71		$960.9101	$960.91	$960.95	$960.90