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	$123.46	11.722%	$137.932	$137.93	$137.95	$137.90
Purchase #2	$46.89	9.339%	$51.2691	$51.27	$51.25	$51.30
Purchase #3	$134.42	5.361%	$141.6263	$141.63	$141.65	$141.60
Purchase #4	$82.90	9.627%	$90.8808	$90.88	$90.90	$90.90
Purchase #5	$71.83	11.636%	$80.1881	$80.19	$80.20	$80.20
Purchase #6	$63.79	13.232%	$72.2307	$72.23	$72.25	$72.20
Purchase #7	$213.43	9.743%	$234.2245	$234.22	$234.20	$234.20
7 purchase totals =	$736.72		$808.3515	$808.35	$808.40	$808.30