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	$180.82	11.619%	$201.8295	$201.83	$201.85	$201.80
Purchase #2	$159.73	9.110%	$174.2814	$174.28	$174.30	$174.30
Purchase #3	$115.69	13.280%	$131.0536	$131.05	$131.05	$131.10
Purchase #4	$164.67	8.782%	$179.1313	$179.13	$179.15	$179.10
Purchase #5	$246.95	11.285%	$274.8183	$274.82	$274.80	$274.80
Purchase #6	$87.89	13.326%	$99.6022	$99.60	$99.60	$99.60
Purchase #7	$122.33	13.677%	$139.0611	$139.06	$139.05	$139.10
7 purchase totals =	$1,078.08		$1,199.7774	$1,199.77	$1,199.80	$1,199.80