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	$51.55	10.111%	$56.7622	$56.76	$56.75	$56.80
Purchase #2	$205.90	6.120%	$218.5011	$218.50	$218.50	$218.50
Purchase #3	$36.37	4.289%	$37.9299	$37.93	$37.95	$37.90
Purchase #4	$208.37	5.544%	$219.922	$219.92	$219.90	$219.90
Purchase #5	$78.55	13.647%	$89.2697	$89.27	$89.25	$89.30
Purchase #6	$179.25	7.481%	$192.6597	$192.66	$192.65	$192.70
Purchase #7	$39.95	12.120%	$44.7919	$44.79	$44.80	$44.80
7 purchase totals =	$799.94		$859.8365	$859.83	$859.80	$859.90