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	$228.32	6.833%	$243.9211	$243.92	$243.90	$243.90
Purchase #2	$131.63	11.535%	$146.8135	$146.81	$146.80	$146.80
Purchase #3	$238.56	10.193%	$262.8764	$262.88	$262.90	$262.90
Purchase #4	$137.52	13.711%	$156.3754	$156.38	$156.40	$156.40
Purchase #5	$242.82	12.585%	$273.3789	$273.38	$273.40	$273.40
Purchase #6	$9.52	8.389%	$10.3186	$10.32	$10.30	$10.30
Purchase #7	$224.98	11.822%	$251.5771	$251.58	$251.60	$251.60
7 purchase totals =	$1,213.35		$1,345.2610	$1,345.27	$1,345.30	$1,345.30