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	$79.60	13.605%	$90.4296	$90.43	$90.45	$90.40
Purchase #2	$37.66	9.305%	$41.1643	$41.16	$41.15	$41.20
Purchase #3	$133.73	3.177%	$137.9786	$137.98	$138.00	$138.00
Purchase #4	$64.38	5.853%	$68.1482	$68.15	$68.15	$68.10
Purchase #5	$199.61	9.165%	$217.9043	$217.90	$217.90	$217.90
Purchase #6	$49.33	13.223%	$55.8529	$55.85	$55.85	$55.90
Purchase #7	$119.46	3.283%	$123.3819	$123.38	$123.40	$123.40
7 purchase totals =	$683.77		$734.8598	$734.85	$734.90	$734.90