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	$81.94	11.192%	$91.1107	$91.11	$91.10	$91.10
Purchase #2	$18.69	10.112%	$20.5799	$20.58	$20.60	$20.60
Purchase #3	$81.42	11.397%	$90.6994	$90.70	$90.70	$90.70
Purchase #4	$14.57	6.772%	$15.5567	$15.56	$15.55	$15.60
Purchase #5	$72.46	8.367%	$78.5227	$78.52	$78.50	$78.50
Purchase #6	$174.98	6.786%	$186.8541	$186.85	$186.85	$186.90
Purchase #7	$113.25	6.395%	$120.4923	$120.49	$120.50	$120.50
7 purchase totals =	$557.31		$603.8158	$603.81	$603.80	$603.90