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	$99.29	12.668%	$111.8681	$111.87	$111.85	$111.90
Purchase #2	$88.49	11.642%	$98.792	$98.79	$98.80	$98.80
Purchase #3	$148.58	13.149%	$168.1168	$168.12	$168.10	$168.10
Purchase #4	$178.59	4.648%	$186.8909	$186.89	$186.90	$186.90
Purchase #5	$167.61	5.190%	$176.309	$176.31	$176.30	$176.30
Purchase #6	$8.96	7.184%	$9.6037	$9.60	$9.60	$9.60
Purchase #7	$140.34	3.254%	$144.9067	$144.91	$144.90	$144.90
7 purchase totals =	$831.86		$896.4872	$896.49	$896.45	$896.50