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	$165.66	12.184%	$185.844	$185.84	$185.85	$185.80
Purchase #2	$141.65	9.653%	$155.3235	$155.32	$155.30	$155.30
Purchase #3	$99.65	13.296%	$112.8995	$112.90	$112.90	$112.90
Purchase #4	$18.37	8.593%	$19.9485	$19.95	$19.95	$19.90
Purchase #5	$171.73	4.587%	$179.6073	$179.61	$179.60	$179.60
Purchase #6	$175.73	13.678%	$199.7663	$199.77	$199.75	$199.80
Purchase #7	$126.39	4.281%	$131.8008	$131.80	$131.80	$131.80
7 purchase totals =	$899.18		$985.1899	$985.19	$985.15	$985.10