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	$69.38	7.470%	$74.5627	$74.56	$74.55	$74.60
Purchase #2	$41.35	13.390%	$46.8868	$46.89	$46.90	$46.90
Purchase #3	$206.29	9.648%	$226.1929	$226.19	$226.20	$226.20
Purchase #4	$72.71	12.191%	$81.5741	$81.57	$81.55	$81.60
Purchase #5	$57.65	9.741%	$63.2657	$63.27	$63.25	$63.30
Purchase #6	$94.25	5.598%	$99.5261	$99.53	$99.55	$99.50
Purchase #7	$80.73	11.789%	$90.2473	$90.25	$90.25	$90.20
7 purchase totals =	$622.36		$682.2556	$682.26	$682.25	$682.30