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	$63.34	13.859%	$72.1183	$72.12	$72.10	$72.10
Purchase #2	$77.58	11.628%	$86.601	$86.60	$86.60	$86.60
Purchase #3	$216.51	10.351%	$238.921	$238.92	$238.90	$238.90
Purchase #4	$220.50	13.772%	$250.8673	$250.87	$250.85	$250.90
Purchase #5	$130.69	9.833%	$143.5407	$143.54	$143.55	$143.50
Purchase #6	$215.60	8.792%	$234.5556	$234.56	$234.55	$234.60
Purchase #7	$221.29	11.411%	$246.5414	$246.54	$246.55	$246.50
7 purchase totals =	$1,145.51		$1,273.1453	$1,273.15	$1,273.10	$1,273.10