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	$156.94	4.641%	$164.2236	$164.22	$164.20	$164.20
Purchase #2	$73.64	5.341%	$77.5731	$77.57	$77.55	$77.60
Purchase #3	$47.54	5.867%	$50.3292	$50.33	$50.35	$50.30
Purchase #4	$47.47	13.464%	$53.8614	$53.86	$53.85	$53.90
Purchase #5	$133.87	4.215%	$139.5126	$139.51	$139.50	$139.50
Purchase #6	$51.35	7.551%	$55.2274	$55.23	$55.25	$55.20
Purchase #7	$38.81	6.422%	$41.3024	$41.30	$41.30	$41.30
7 purchase totals =	$549.62		$582.0297	$582.02	$582.00	$582.00