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	$234.65	3.538%	$242.9519	$242.95	$242.95	$243.00
Purchase #2	$55.68	3.691%	$57.7351	$57.74	$57.75	$57.70
Purchase #3	$70.51	10.396%	$77.8402	$77.84	$77.85	$77.80
Purchase #4	$248.27	12.163%	$278.4671	$278.47	$278.45	$278.50
Purchase #5	$64.59	8.111%	$69.8289	$69.83	$69.85	$69.80
Purchase #6	$82.34	9.857%	$90.4563	$90.46	$90.45	$90.50
Purchase #7	$39.86	3.446%	$41.2336	$41.23	$41.25	$41.20
7 purchase totals =	$795.90		$858.5131	$858.52	$858.55	$858.50