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	$249.69	11.671%	$278.8313	$278.83	$278.85	$278.80
Purchase #2	$213.62	11.784%	$238.793	$238.79	$238.80	$238.80
Purchase #3	$198.39	12.331%	$222.8535	$222.85	$222.85	$222.90
Purchase #4	$28.35	3.870%	$29.4471	$29.45	$29.45	$29.40
Purchase #5	$93.66	4.519%	$97.8925	$97.89	$97.90	$97.90
Purchase #6	$62.40	7.830%	$67.2859	$67.29	$67.30	$67.30
Purchase #7	$59.83	12.763%	$67.4661	$67.47	$67.45	$67.50
7 purchase totals =	$905.94		$1,002.5694	$1,002.57	$1,002.60	$1,002.60