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	$89.52	11.196%	$99.5427	$99.54	$99.55	$99.50
Purchase #2	$19.42	8.537%	$21.0779	$21.08	$21.10	$21.10
Purchase #3	$37.66	5.193%	$39.6157	$39.62	$39.60	$39.60
Purchase #4	$98.60	6.701%	$105.2072	$105.21	$105.20	$105.20
Purchase #5	$118.77	10.861%	$131.6696	$131.67	$131.65	$131.70
Purchase #6	$203.83	8.148%	$220.4381	$220.44	$220.45	$220.40
Purchase #7	$238.31	3.170%	$245.8644	$245.86	$245.85	$245.90
7 purchase totals =	$806.11		$863.4156	$863.42	$863.40	$863.40