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	$234.91	10.392%	$259.3218	$259.32	$259.30	$259.30
Purchase #2	$186.40	7.347%	$200.0948	$200.09	$200.10	$200.10
Purchase #3	$5.89	6.691%	$6.2841	$6.28	$6.30	$6.30
Purchase #4	$247.85	11.541%	$276.4544	$276.45	$276.45	$276.50
Purchase #5	$137.94	6.733%	$147.2275	$147.23	$147.25	$147.20
Purchase #6	$72.39	13.778%	$82.3639	$82.36	$82.35	$82.40
Purchase #7	$35.25	13.207%	$39.9055	$39.91	$39.90	$39.90
7 purchase totals =	$920.63		$1,011.6520	$1,011.64	$1,011.65	$1,011.70