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	$177.72	5.385%	$187.2902	$187.29	$187.30	$187.30
Purchase #2	$209.30	3.874%	$217.4083	$217.41	$217.40	$217.40
Purchase #3	$104.62	13.272%	$118.5052	$118.51	$118.50	$118.50
Purchase #4	$69.34	10.862%	$76.8717	$76.87	$76.85	$76.90
Purchase #5	$162.58	10.625%	$179.8541	$179.85	$179.85	$179.90
Purchase #6	$43.59	5.397%	$45.9426	$45.94	$45.95	$45.90
Purchase #7	$17.65	13.565%	$20.0442	$20.04	$20.05	$20.00
7 purchase totals =	$784.80		$845.9163	$845.91	$845.90	$845.90