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	$250.34	4.399%	$261.3525	$261.35	$261.35	$261.40
Purchase #2	$175.86	7.195%	$188.5131	$188.51	$188.50	$188.50
Purchase #3	$153.52	10.393%	$169.4753	$169.48	$169.50	$169.50
Purchase #4	$97.59	12.574%	$109.861	$109.86	$109.85	$109.90
Purchase #5	$29.47	5.716%	$31.1545	$31.15	$31.15	$31.20
Purchase #6	$22.32	10.423%	$24.6464	$24.65	$24.65	$24.60
Purchase #7	$48.72	10.121%	$53.651	$53.65	$53.65	$53.70
7 purchase totals =	$777.82		$838.6538	$838.65	$838.65	$838.80