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	$45.45	3.633%	$47.1012	$47.10	$47.10	$47.10
Purchase #2	$221.79	8.334%	$240.274	$240.27	$240.25	$240.30
Purchase #3	$42.77	9.602%	$46.8768	$46.88	$46.90	$46.90
Purchase #4	$172.59	10.645%	$190.9622	$190.96	$190.95	$191.00
Purchase #5	$19.59	11.863%	$21.914	$21.91	$21.90	$21.90
Purchase #6	$108.40	10.773%	$120.0779	$120.08	$120.10	$120.10
Purchase #7	$66.69	7.770%	$71.8718	$71.87	$71.85	$71.90
7 purchase totals =	$677.28		$739.0779	$739.07	$739.05	$739.20