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	$94.28	6.393%	$100.3073	$100.31	$100.30	$100.30
Purchase #2	$241.54	9.637%	$264.8172	$264.82	$264.80	$264.80
Purchase #3	$208.30	9.222%	$227.5094	$227.51	$227.50	$227.50
Purchase #4	$211.46	8.262%	$228.9308	$228.93	$228.95	$228.90
Purchase #5	$191.76	7.317%	$205.7911	$205.79	$205.80	$205.80
Purchase #6	$120.34	6.175%	$127.771	$127.77	$127.75	$127.80
Purchase #7	$47.25	3.720%	$49.0077	$49.01	$49.00	$49.00
7 purchase totals =	$1,114.93		$1,204.1345	$1,204.14	$1,204.10	$1,204.10