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	$83.26	7.869%	$89.8117	$89.81	$89.80	$89.80
Purchase #2	$106.28	9.288%	$116.1513	$116.15	$116.15	$116.20
Purchase #3	$236.93	7.435%	$254.5457	$254.55	$254.55	$254.50
Purchase #4	$79.88	13.693%	$90.818	$90.82	$90.80	$90.80
Purchase #5	$107.68	5.663%	$113.7779	$113.78	$113.80	$113.80
Purchase #6	$87.48	3.542%	$90.5785	$90.58	$90.60	$90.60
Purchase #7	$159.45	7.736%	$171.7851	$171.79	$171.80	$171.80
7 purchase totals =	$860.96		$927.4682	$927.48	$927.50	$927.50