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	$140.73	3.313%	$145.3924	$145.39	$145.40	$145.40
Purchase #2	$174.65	12.618%	$196.6873	$196.69	$196.70	$196.70
Purchase #3	$13.72	7.616%	$14.7649	$14.76	$14.75	$14.80
Purchase #4	$46.76	13.159%	$52.9131	$52.91	$52.90	$52.90
Purchase #5	$53.34	10.486%	$58.9332	$58.93	$58.95	$58.90
Purchase #6	$205.48	12.162%	$230.4705	$230.47	$230.45	$230.50
Purchase #7	$35.42	13.640%	$40.2513	$40.25	$40.25	$40.30
7 purchase totals =	$670.10		$739.4127	$739.40	$739.40	$739.50