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	$30.56	6.829%	$32.6469	$32.65	$32.65	$32.60
Purchase #2	$73.84	13.538%	$83.8365	$83.84	$83.85	$83.80
Purchase #3	$131.94	5.636%	$139.3761	$139.38	$139.40	$139.40
Purchase #4	$90.91	6.798%	$97.0901	$97.09	$97.10	$97.10
Purchase #5	$76.34	11.355%	$85.0084	$85.01	$85.00	$85.00
Purchase #6	$182.86	4.339%	$190.7943	$190.79	$190.80	$190.80
Purchase #7	$51.85	10.185%	$57.1309	$57.13	$57.15	$57.10
7 purchase totals =	$638.30		$685.8832	$685.89	$685.95	$685.80