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	$76.50	8.307%	$82.8549	$82.85	$82.85	$82.90
Purchase #2	$240.98	13.174%	$272.7267	$272.73	$272.75	$272.70
Purchase #3	$192.39	4.436%	$200.9244	$200.92	$200.90	$200.90
Purchase #4	$72.35	12.540%	$81.4227	$81.42	$81.40	$81.40
Purchase #5	$89.78	7.282%	$96.3178	$96.32	$96.30	$96.30
Purchase #6	$14.70	8.284%	$15.9177	$15.92	$15.90	$15.90
Purchase #7	$53.99	10.665%	$59.748	$59.75	$59.75	$59.70
7 purchase totals =	$740.69		$809.9122	$809.91	$809.85	$809.80