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	$11.84	6.863%	$12.6526	$12.65	$12.65	$12.70
Purchase #2	$119.33	4.355%	$124.5268	$124.53	$124.55	$124.50
Purchase #3	$64.59	4.324%	$67.3829	$67.38	$67.40	$67.40
Purchase #4	$140.31	3.722%	$145.5323	$145.53	$145.55	$145.50
Purchase #5	$93.93	10.818%	$104.0913	$104.09	$104.10	$104.10
Purchase #6	$28.62	11.713%	$31.9723	$31.97	$31.95	$32.00
Purchase #7	$117.48	8.765%	$127.7771	$127.78	$127.80	$127.80
7 purchase totals =	$576.10		$613.9353	$613.93	$614.00	$614.00