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	$103.26	6.122%	$109.5816	$109.58	$109.60	$109.60
Purchase #2	$109.40	3.761%	$113.5145	$113.51	$113.50	$113.50
Purchase #3	$167.39	11.676%	$186.9345	$186.93	$186.95	$186.90
Purchase #4	$46.85	9.796%	$51.4394	$51.44	$51.45	$51.40
Purchase #5	$78.60	13.380%	$89.1167	$89.12	$89.10	$89.10
Purchase #6	$137.46	8.336%	$148.9187	$148.92	$148.90	$148.90
Purchase #7	$81.93	11.388%	$91.2602	$91.26	$91.25	$91.30
7 purchase totals =	$724.89		$790.7656	$790.76	$790.75	$790.70