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	$51.68	13.176%	$58.4894	$58.49	$58.50	$58.50
Purchase #2	$18.35	4.366%	$19.1512	$19.15	$19.15	$19.20
Purchase #3	$240.80	12.345%	$270.5268	$270.53	$270.55	$270.50
Purchase #4	$73.33	6.445%	$78.0561	$78.06	$78.05	$78.10
Purchase #5	$188.38	12.253%	$211.4622	$211.46	$211.45	$211.50
Purchase #6	$58.25	7.428%	$62.5768	$62.58	$62.60	$62.60
Purchase #7	$137.77	7.841%	$148.5725	$148.57	$148.55	$148.60
7 purchase totals =	$768.56		$848.8350	$848.84	$848.85	$849.00