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	$31.40	6.867%	$33.5562	$33.56	$33.55	$33.60
Purchase #2	$196.72	12.112%	$220.5467	$220.55	$220.55	$220.50
Purchase #3	$93.49	8.658%	$101.5844	$101.58	$101.60	$101.60
Purchase #4	$123.79	8.518%	$134.3344	$134.33	$134.35	$134.30
Purchase #5	$223.60	10.430%	$246.9215	$246.92	$246.90	$246.90
Purchase #6	$41.43	10.244%	$45.6741	$45.67	$45.65	$45.70
Purchase #7	$107.49	3.514%	$111.2672	$111.27	$111.25	$111.30
7 purchase totals =	$817.92		$893.8845	$893.88	$893.85	$893.90