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	$131.99	11.188%	$146.757	$146.76	$146.75	$146.80
Purchase #2	$126.73	6.782%	$135.3248	$135.32	$135.30	$135.30
Purchase #3	$228.94	5.490%	$241.5088	$241.51	$241.50	$241.50
Purchase #4	$55.49	7.139%	$59.4514	$59.45	$59.45	$59.50
Purchase #5	$217.91	4.812%	$228.3958	$228.40	$228.40	$228.40
Purchase #6	$38.86	4.504%	$40.6103	$40.61	$40.60	$40.60
Purchase #7	$126.80	12.342%	$142.4497	$142.45	$142.45	$142.40
7 purchase totals =	$926.72		$994.4978	$994.50	$994.45	$994.50