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	$143.94	8.769%	$156.5621	$156.56	$156.55	$156.60
Purchase #2	$50.83	3.239%	$52.4764	$52.48	$52.50	$52.50
Purchase #3	$115.48	11.629%	$128.9092	$128.91	$128.90	$128.90
Purchase #4	$15.71	6.435%	$16.7209	$16.72	$16.70	$16.70
Purchase #5	$19.88	8.321%	$21.5342	$21.53	$21.55	$21.50
Purchase #6	$205.51	5.454%	$216.7185	$216.72	$216.70	$216.70
Purchase #7	$38.81	3.740%	$40.2615	$40.26	$40.25	$40.30
7 purchase totals =	$590.16		$633.1828	$633.18	$633.15	$633.20