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	$241.91	13.210%	$273.8663	$273.87	$273.85	$273.90
Purchase #2	$25.95	5.615%	$27.4071	$27.41	$27.40	$27.40
Purchase #3	$217.82	11.236%	$242.2943	$242.29	$242.30	$242.30
Purchase #4	$68.26	6.811%	$72.9092	$72.91	$72.90	$72.90
Purchase #5	$17.43	4.158%	$18.1547	$18.15	$18.15	$18.20
Purchase #6	$36.95	10.154%	$40.7019	$40.70	$40.70	$40.70
Purchase #7	$25.38	12.237%	$28.4858	$28.49	$28.50	$28.50
7 purchase totals =	$633.70		$703.8193	$703.82	$703.80	$703.90