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	$236.85	11.652%	$264.4478	$264.45	$264.45	$264.40
Purchase #2	$57.45	3.816%	$59.6423	$59.64	$59.65	$59.60
Purchase #3	$26.33	12.437%	$29.6047	$29.60	$29.60	$29.60
Purchase #4	$79.55	5.866%	$84.2164	$84.22	$84.20	$84.20
Purchase #5	$72.59	6.547%	$77.3425	$77.34	$77.35	$77.30
Purchase #6	$58.34	7.677%	$62.8188	$62.82	$62.80	$62.80
Purchase #7	$81.54	5.178%	$85.7621	$85.76	$85.75	$85.80
7 purchase totals =	$612.65		$663.8346	$663.83	$663.80	$663.70