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	$169.67	11.211%	$188.6917	$188.69	$188.70	$188.70
Purchase #2	$36.63	9.497%	$40.1088	$40.11	$40.10	$40.10
Purchase #3	$95.93	4.567%	$100.3111	$100.31	$100.30	$100.30
Purchase #4	$214.41	6.264%	$227.8406	$227.84	$227.85	$227.80
Purchase #5	$249.60	8.724%	$271.3751	$271.38	$271.40	$271.40
Purchase #6	$119.69	10.736%	$132.5399	$132.54	$132.55	$132.50
Purchase #7	$40.69	4.841%	$42.6598	$42.66	$42.65	$42.70
7 purchase totals =	$926.62		$1,003.5270	$1,003.53	$1,003.55	$1,003.50