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	$97.40	7.172%	$104.3855	$104.39	$104.40	$104.40
Purchase #2	$54.34	9.281%	$59.3833	$59.38	$59.40	$59.40
Purchase #3	$138.77	10.513%	$153.3589	$153.36	$153.35	$153.40
Purchase #4	$191.94	12.368%	$215.6791	$215.68	$215.70	$215.70
Purchase #5	$48.71	5.860%	$51.5644	$51.56	$51.55	$51.60
Purchase #6	$145.81	11.413%	$162.4513	$162.45	$162.45	$162.50
Purchase #7	$28.81	11.405%	$32.0958	$32.10	$32.10	$32.10
7 purchase totals =	$705.78		$778.9183	$778.92	$778.95	$779.10