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	$87.44	12.682%	$98.5291	$98.53	$98.55	$98.50
Purchase #2	$98.69	3.244%	$101.8915	$101.89	$101.90	$101.90
Purchase #3	$93.79	12.242%	$105.2718	$105.27	$105.25	$105.30
Purchase #4	$43.99	4.387%	$45.9198	$45.92	$45.90	$45.90
Purchase #5	$234.59	6.817%	$250.582	$250.58	$250.60	$250.60
Purchase #6	$183.69	5.831%	$194.401	$194.40	$194.40	$194.40
Purchase #7	$101.31	9.156%	$110.5859	$110.59	$110.60	$110.60
7 purchase totals =	$843.50		$907.1811	$907.18	$907.20	$907.20