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	$41.45	4.264%	$43.2174	$43.22	$43.20	$43.20
Purchase #2	$93.90	8.789%	$102.1529	$102.15	$102.15	$102.20
Purchase #3	$29.70	12.537%	$33.4235	$33.42	$33.40	$33.40
Purchase #4	$219.40	8.662%	$238.4044	$238.40	$238.40	$238.40
Purchase #5	$136.97	6.795%	$146.2771	$146.28	$146.30	$146.30
Purchase #6	$27.80	7.402%	$29.8578	$29.86	$29.85	$29.90
Purchase #7	$53.28	12.446%	$59.9112	$59.91	$59.90	$59.90
7 purchase totals =	$602.50		$653.2443	$653.24	$653.20	$653.30