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	$50.86	9.115%	$55.4959	$55.50	$55.50	$55.50
Purchase #2	$89.95	12.561%	$101.2486	$101.25	$101.25	$101.20
Purchase #3	$89.58	10.830%	$99.2815	$99.28	$99.30	$99.30
Purchase #4	$207.37	12.861%	$234.0399	$234.04	$234.05	$234.00
Purchase #5	$33.67	11.351%	$37.4919	$37.49	$37.50	$37.50
Purchase #6	$46.99	7.304%	$50.4221	$50.42	$50.40	$50.40
Purchase #7	$135.92	5.872%	$143.9012	$143.90	$143.90	$143.90
7 purchase totals =	$654.34		$721.8811	$721.88	$721.90	$721.80