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	$245.56	13.703%	$279.2091	$279.21	$279.20	$279.20
Purchase #2	$85.72	5.278%	$90.2443	$90.24	$90.25	$90.20
Purchase #3	$202.69	10.737%	$224.4528	$224.45	$224.45	$224.50
Purchase #4	$83.66	12.501%	$94.1183	$94.12	$94.10	$94.10
Purchase #5	$118.79	10.208%	$130.9161	$130.92	$130.90	$130.90
Purchase #6	$207.76	7.322%	$222.9722	$222.97	$222.95	$223.00
Purchase #7	$72.39	12.585%	$81.5003	$81.50	$81.50	$81.50
7 purchase totals =	$1,016.57		$1,123.4131	$1,123.41	$1,123.35	$1,123.40