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	$77.46	12.114%	$86.8435	$86.84	$86.85	$86.80
Purchase #2	$123.90	4.545%	$129.5313	$129.53	$129.55	$129.50
Purchase #3	$90.54	10.326%	$99.8892	$99.89	$99.90	$99.90
Purchase #4	$15.54	10.311%	$17.1423	$17.14	$17.15	$17.10
Purchase #5	$130.75	12.845%	$147.5448	$147.54	$147.55	$147.50
Purchase #6	$90.81	6.842%	$97.0232	$97.02	$97.00	$97.00
Purchase #7	$63.26	11.222%	$70.359	$70.36	$70.35	$70.40
7 purchase totals =	$592.26		$648.3333	$648.32	$648.35	$648.20