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	$86.78	4.502%	$90.6868	$90.69	$90.70	$90.70
Purchase #2	$123.95	12.183%	$139.0508	$139.05	$139.05	$139.10
Purchase #3	$196.99	6.596%	$209.9835	$209.98	$210.00	$210.00
Purchase #4	$13.38	3.619%	$13.8642	$13.86	$13.85	$13.90
Purchase #5	$246.67	5.184%	$259.4574	$259.46	$259.45	$259.50
Purchase #6	$95.96	9.235%	$104.8219	$104.82	$104.80	$104.80
Purchase #7	$53.69	6.540%	$57.2013	$57.20	$57.20	$57.20
7 purchase totals =	$817.42		$875.0659	$875.06	$875.05	$875.20