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	$99.30	12.731%	$111.9419	$111.94	$111.95	$111.90
Purchase #2	$193.26	3.646%	$200.3063	$200.31	$200.30	$200.30
Purchase #3	$81.81	12.846%	$92.3193	$92.32	$92.30	$92.30
Purchase #4	$103.48	7.504%	$111.2451	$111.25	$111.25	$111.20
Purchase #5	$107.87	10.531%	$119.2298	$119.23	$119.25	$119.20
Purchase #6	$191.61	11.306%	$213.2734	$213.27	$213.25	$213.30
Purchase #7	$34.66	13.412%	$39.3086	$39.31	$39.30	$39.30
7 purchase totals =	$811.99		$887.6244	$887.63	$887.60	$887.50