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	$89.94	10.161%	$99.0788	$99.08	$99.10	$99.10
Purchase #2	$71.94	12.236%	$80.7426	$80.74	$80.75	$80.70
Purchase #3	$38.83	4.510%	$40.5812	$40.58	$40.60	$40.60
Purchase #4	$240.51	12.578%	$270.7613	$270.76	$270.75	$270.80
Purchase #5	$184.63	3.267%	$190.6619	$190.66	$190.65	$190.70
Purchase #6	$201.40	7.728%	$216.9642	$216.96	$216.95	$217.00
Purchase #7	$142.67	12.233%	$160.1228	$160.12	$160.10	$160.10
7 purchase totals =	$969.92		$1,058.9128	$1,058.90	$1,058.90	$1,059.00