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	$243.99	6.106%	$258.888	$258.89	$258.90	$258.90
Purchase #2	$233.35	9.664%	$255.9009	$255.90	$255.90	$255.90
Purchase #3	$35.49	10.774%	$39.3137	$39.31	$39.30	$39.30
Purchase #4	$64.40	12.694%	$72.5749	$72.57	$72.55	$72.60
Purchase #5	$39.59	8.109%	$42.8004	$42.80	$42.80	$42.80
Purchase #6	$19.36	12.733%	$21.8251	$21.83	$21.85	$21.80
Purchase #7	$62.86	11.160%	$69.8752	$69.88	$69.90	$69.90
7 purchase totals =	$699.04		$761.1782	$761.18	$761.20	$761.20