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	$105.66	7.684%	$113.7789	$113.78	$113.80	$113.80
Purchase #2	$93.26	10.645%	$103.1875	$103.19	$103.20	$103.20
Purchase #3	$243.81	6.380%	$259.3651	$259.37	$259.35	$259.40
Purchase #4	$70.74	8.318%	$76.6242	$76.62	$76.60	$76.60
Purchase #5	$249.82	12.116%	$280.0882	$280.09	$280.10	$280.10
Purchase #6	$178.37	4.360%	$186.1469	$186.15	$186.15	$186.10
Purchase #7	$73.46	10.335%	$81.0521	$81.05	$81.05	$81.10
7 purchase totals =	$1,015.12		$1,100.2429	$1,100.25	$1,100.25	$1,100.30