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	$66.54	10.661%	$73.6338	$73.63	$73.65	$73.60
Purchase #2	$114.75	4.343%	$119.7336	$119.73	$119.75	$119.70
Purchase #3	$72.39	7.360%	$77.7179	$77.72	$77.70	$77.70
Purchase #4	$143.71	5.112%	$151.0565	$151.06	$151.05	$151.10
Purchase #5	$18.82	9.651%	$20.6363	$20.64	$20.65	$20.60
Purchase #6	$19.64	7.259%	$21.0657	$21.07	$21.05	$21.10
Purchase #7	$209.69	3.184%	$216.3665	$216.37	$216.35	$216.40
7 purchase totals =	$645.54		$680.2103	$680.22	$680.20	$680.20