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	$143.34	11.574%	$159.9302	$159.93	$159.95	$159.90
Purchase #2	$121.27	5.334%	$127.7385	$127.74	$127.75	$127.70
Purchase #3	$104.77	3.511%	$108.4485	$108.45	$108.45	$108.40
Purchase #4	$16.97	9.269%	$18.5429	$18.54	$18.55	$18.50
Purchase #5	$57.55	10.152%	$63.3925	$63.39	$63.40	$63.40
Purchase #6	$70.56	13.401%	$80.0157	$80.02	$80.00	$80.00
Purchase #7	$65.98	10.544%	$72.9369	$72.94	$72.95	$72.90
7 purchase totals =	$580.44		$631.0052	$631.01	$631.05	$630.80