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	$159.55	4.313%	$166.4314	$166.43	$166.45	$166.40
Purchase #2	$181.54	8.291%	$196.5915	$196.59	$196.60	$196.60
Purchase #3	$147.72	13.806%	$168.1142	$168.11	$168.10	$168.10
Purchase #4	$9.27	6.746%	$9.8954	$9.90	$9.90	$9.90
Purchase #5	$165.87	13.660%	$188.5278	$188.53	$188.55	$188.50
Purchase #6	$29.90	4.819%	$31.3409	$31.34	$31.35	$31.30
Purchase #7	$212.63	11.282%	$236.6189	$236.62	$236.60	$236.60
7 purchase totals =	$906.48		$997.5201	$997.52	$997.55	$997.40