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	$249.47	12.430%	$280.4791	$280.48	$280.50	$280.50
Purchase #2	$173.32	6.505%	$184.5945	$184.59	$184.60	$184.60
Purchase #3	$50.67	7.210%	$54.3233	$54.32	$54.30	$54.30
Purchase #4	$98.83	13.724%	$112.3934	$112.39	$112.40	$112.40
Purchase #5	$115.72	11.331%	$128.8322	$128.83	$128.85	$128.80
Purchase #6	$87.79	5.224%	$92.3761	$92.38	$92.40	$92.40
Purchase #7	$57.75	3.157%	$59.5732	$59.57	$59.55	$59.60
7 purchase totals =	$833.55		$912.5718	$912.56	$912.60	$912.60