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	$109.86	5.665%	$116.0836	$116.08	$116.10	$116.10
Purchase #2	$90.85	6.585%	$96.8325	$96.83	$96.85	$96.80
Purchase #3	$6.74	12.605%	$7.5896	$7.59	$7.60	$7.60
Purchase #4	$248.81	7.575%	$267.6574	$267.66	$267.65	$267.70
Purchase #5	$136.70	10.681%	$151.3009	$151.30	$151.30	$151.30
Purchase #6	$52.58	6.287%	$55.8857	$55.89	$55.90	$55.90
Purchase #7	$216.77	7.299%	$232.592	$232.59	$232.60	$232.60
7 purchase totals =	$862.31		$927.9417	$927.94	$928.00	$928.00