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	$141.86	5.766%	$150.0396	$150.04	$150.05	$150.00
Purchase #2	$158.34	9.160%	$172.8439	$172.84	$172.85	$172.80
Purchase #3	$83.32	7.712%	$89.7456	$89.75	$89.75	$89.70
Purchase #4	$122.91	7.161%	$131.7116	$131.71	$131.70	$131.70
Purchase #5	$73.25	12.457%	$82.3748	$82.37	$82.35	$82.40
Purchase #6	$54.46	4.572%	$56.9499	$56.95	$56.95	$56.90
Purchase #7	$230.25	5.626%	$243.2039	$243.20	$243.20	$243.20
7 purchase totals =	$864.39		$926.8693	$926.86	$926.85	$926.70