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	$245.54	4.216%	$255.892	$255.89	$255.90	$255.90
Purchase #2	$60.93	10.199%	$67.1443	$67.14	$67.15	$67.10
Purchase #3	$61.55	8.374%	$66.7042	$66.70	$66.70	$66.70
Purchase #4	$216.90	12.309%	$243.5982	$243.60	$243.60	$243.60
Purchase #5	$190.92	12.287%	$214.3783	$214.38	$214.40	$214.40
Purchase #6	$139.42	3.498%	$144.2969	$144.30	$144.30	$144.30
Purchase #7	$15.55	10.338%	$17.1576	$17.16	$17.15	$17.20
7 purchase totals =	$930.81		$1,009.1715	$1,009.17	$1,009.20	$1,009.20