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	$55.89	4.773%	$58.5576	$58.56	$58.55	$58.60
Purchase #2	$64.96	11.486%	$72.4213	$72.42	$72.40	$72.40
Purchase #3	$126.69	12.314%	$142.2906	$142.29	$142.30	$142.30
Purchase #4	$238.68	10.534%	$263.8226	$263.82	$263.80	$263.80
Purchase #5	$140.54	3.159%	$144.9797	$144.98	$145.00	$145.00
Purchase #6	$121.38	10.548%	$134.1832	$134.18	$134.20	$134.20
Purchase #7	$157.41	10.830%	$174.4575	$174.46	$174.45	$174.50
7 purchase totals =	$905.55		$990.7125	$990.71	$990.70	$990.80