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	$11.45	12.845%	$12.9208	$12.92	$12.90	$12.90
Purchase #2	$208.48	8.364%	$225.9173	$225.92	$225.90	$225.90
Purchase #3	$249.82	12.282%	$280.5029	$280.50	$280.50	$280.50
Purchase #4	$132.63	7.724%	$142.8743	$142.87	$142.85	$142.90
Purchase #5	$227.95	4.183%	$237.4851	$237.49	$237.50	$237.50
Purchase #6	$130.32	10.759%	$144.3411	$144.34	$144.35	$144.30
Purchase #7	$64.96	11.274%	$72.2836	$72.28	$72.30	$72.30
7 purchase totals =	$1,025.61		$1,116.3251	$1,116.32	$1,116.30	$1,116.30