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	$118.56	4.184%	$123.5206	$123.52	$123.50	$123.50
Purchase #2	$75.58	8.811%	$82.2394	$82.24	$82.25	$82.20
Purchase #3	$125.25	7.716%	$134.9143	$134.91	$134.90	$134.90
Purchase #4	$169.69	13.284%	$192.2316	$192.23	$192.25	$192.20
Purchase #5	$60.95	9.175%	$66.5422	$66.54	$66.55	$66.50
Purchase #6	$172.82	9.229%	$188.7696	$188.77	$188.75	$188.80
Purchase #7	$98.37	3.665%	$101.9753	$101.98	$102.00	$102.00
7 purchase totals =	$821.22		$890.1930	$890.19	$890.20	$890.10