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	$160.83	5.190%	$169.1771	$169.18	$169.20	$169.20
Purchase #2	$233.46	9.854%	$256.4651	$256.47	$256.45	$256.50
Purchase #3	$168.77	8.406%	$182.9568	$182.96	$182.95	$183.00
Purchase #4	$48.61	10.250%	$53.5925	$53.59	$53.60	$53.60
Purchase #5	$74.55	6.660%	$79.515	$79.52	$79.50	$79.50
Purchase #6	$234.54	7.327%	$251.7247	$251.72	$251.70	$251.70
Purchase #7	$172.97	9.528%	$189.4506	$189.45	$189.45	$189.50
7 purchase totals =	$1,093.73		$1,182.8818	$1,182.89	$1,182.85	$1,183.00