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	$84.84	6.614%	$90.4513	$90.45	$90.45	$90.50
Purchase #2	$46.55	13.625%	$52.8924	$52.89	$52.90	$52.90
Purchase #3	$146.78	12.342%	$164.8956	$164.90	$164.90	$164.90
Purchase #4	$107.31	9.456%	$117.4572	$117.46	$117.45	$117.50
Purchase #5	$14.62	13.112%	$16.537	$16.54	$16.55	$16.50
Purchase #6	$194.78	5.241%	$204.9884	$204.99	$205.00	$205.00
Purchase #7	$47.89	8.821%	$52.1144	$52.11	$52.10	$52.10
7 purchase totals =	$642.77		$699.3363	$699.34	$699.35	$699.40