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	$89.87	10.856%	$99.6263	$99.63	$99.65	$99.60
Purchase #2	$18.59	9.372%	$20.3323	$20.33	$20.35	$20.30
Purchase #3	$66.34	10.824%	$73.5206	$73.52	$73.50	$73.50
Purchase #4	$209.41	13.509%	$237.6992	$237.70	$237.70	$237.70
Purchase #5	$188.58	6.397%	$200.6435	$200.64	$200.65	$200.60
Purchase #6	$141.50	10.437%	$156.2684	$156.27	$156.25	$156.30
Purchase #7	$199.85	4.758%	$209.3589	$209.36	$209.35	$209.40
7 purchase totals =	$914.14		$997.4492	$997.45	$997.45	$997.40