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	$15.73	11.370%	$17.5185	$17.52	$17.50	$17.50
Purchase #2	$41.58	10.223%	$45.8307	$45.83	$45.85	$45.80
Purchase #3	$210.72	13.330%	$238.809	$238.81	$238.80	$238.80
Purchase #4	$229.32	7.422%	$246.3401	$246.34	$246.35	$246.30
Purchase #5	$153.40	7.830%	$165.4112	$165.41	$165.40	$165.40
Purchase #6	$182.65	5.126%	$192.0126	$192.01	$192.00	$192.00
Purchase #7	$53.92	9.433%	$59.0063	$59.01	$59.00	$59.00
7 purchase totals =	$887.32		$964.9284	$964.93	$964.90	$964.80