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	$20.87	12.446%	$23.4675	$23.47	$23.45	$23.50
Purchase #2	$64.49	12.865%	$72.7866	$72.79	$72.80	$72.80
Purchase #3	$127.44	13.420%	$144.5424	$144.54	$144.55	$144.50
Purchase #4	$206.86	6.413%	$220.1259	$220.13	$220.15	$220.10
Purchase #5	$243.90	12.300%	$273.8997	$273.90	$273.90	$273.90
Purchase #6	$16.82	6.133%	$17.8516	$17.85	$17.85	$17.90
Purchase #7	$89.35	10.706%	$98.9158	$98.92	$98.90	$98.90
7 purchase totals =	$769.73		$851.5895	$851.60	$851.60	$851.60