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	$78.67	5.359%	$82.8859	$82.89	$82.90	$82.90
Purchase #2	$26.72	6.161%	$28.3662	$28.37	$28.35	$28.40
Purchase #3	$173.94	3.374%	$179.8087	$179.81	$179.80	$179.80
Purchase #4	$77.45	7.738%	$83.4431	$83.44	$83.45	$83.40
Purchase #5	$180.60	8.874%	$196.6264	$196.63	$196.65	$196.60
Purchase #6	$19.33	9.574%	$21.1807	$21.18	$21.20	$21.20
Purchase #7	$219.57	9.798%	$241.0835	$241.08	$241.10	$241.10
7 purchase totals =	$776.28		$833.3945	$833.40	$833.45	$833.40