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	$237.93	11.734%	$265.8487	$265.85	$265.85	$265.80
Purchase #2	$18.42	10.390%	$20.3338	$20.33	$20.35	$20.30
Purchase #3	$50.46	3.747%	$52.3507	$52.35	$52.35	$52.40
Purchase #4	$166.32	6.317%	$176.8264	$176.83	$176.85	$176.80
Purchase #5	$30.66	9.823%	$33.6717	$33.67	$33.65	$33.70
Purchase #6	$145.30	7.648%	$156.4125	$156.41	$156.40	$156.40
Purchase #7	$74.99	4.220%	$78.1546	$78.15	$78.15	$78.20
7 purchase totals =	$724.08		$783.5984	$783.59	$783.60	$783.60