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	$19.94	9.407%	$21.8158	$21.82	$21.80	$21.80
Purchase #2	$121.51	10.566%	$134.3487	$134.35	$134.35	$134.30
Purchase #3	$237.90	5.248%	$250.385	$250.39	$250.40	$250.40
Purchase #4	$249.86	8.583%	$271.3055	$271.31	$271.30	$271.30
Purchase #5	$233.80	7.321%	$250.9165	$250.92	$250.90	$250.90
Purchase #6	$12.96	3.111%	$13.3632	$13.36	$13.35	$13.40
Purchase #7	$207.66	7.177%	$222.5638	$222.56	$222.55	$222.60
7 purchase totals =	$1,083.63		$1,164.6985	$1,164.71	$1,164.65	$1,164.70