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	$89.35	13.208%	$101.1513	$101.15	$101.15	$101.20
Purchase #2	$226.92	3.459%	$234.7692	$234.77	$234.75	$234.80
Purchase #3	$127.55	12.215%	$143.1302	$143.13	$143.15	$143.10
Purchase #4	$186.82	13.603%	$212.2331	$212.23	$212.25	$212.20
Purchase #5	$205.40	9.473%	$224.8575	$224.86	$224.85	$224.90
Purchase #6	$31.44	10.387%	$34.7057	$34.71	$34.70	$34.70
Purchase #7	$178.55	6.570%	$190.2807	$190.28	$190.30	$190.30
7 purchase totals =	$1,046.03		$1,141.1277	$1,141.13	$1,141.15	$1,141.20