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	$150.89	10.355%	$166.5147	$166.51	$166.50	$166.50
Purchase #2	$50.63	3.396%	$52.3494	$52.35	$52.35	$52.30
Purchase #3	$198.90	8.402%	$215.6116	$215.61	$215.60	$215.60
Purchase #4	$169.41	13.282%	$191.911	$191.91	$191.90	$191.90
Purchase #5	$68.32	4.453%	$71.3623	$71.36	$71.35	$71.40
Purchase #6	$169.87	9.273%	$185.622	$185.62	$185.60	$185.60
Purchase #7	$21.77	6.786%	$23.2473	$23.25	$23.25	$23.20
7 purchase totals =	$829.79		$906.6183	$906.61	$906.55	$906.50