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	$120.54	13.705%	$137.06	$137.06	$137.05	$137.10
Purchase #2	$104.25	4.862%	$109.3186	$109.32	$109.30	$109.30
Purchase #3	$128.58	8.427%	$139.4154	$139.42	$139.40	$139.40
Purchase #4	$70.32	4.694%	$73.6208	$73.62	$73.60	$73.60
Purchase #5	$125.79	5.822%	$133.1135	$133.11	$133.10	$133.10
Purchase #6	$150.89	10.323%	$166.4664	$166.47	$166.45	$166.50
Purchase #7	$206.32	13.683%	$234.5508	$234.55	$234.55	$234.60
7 purchase totals =	$906.69		$993.5455	$993.55	$993.45	$993.60