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	$127.43	13.169%	$144.2113	$144.21	$144.20	$144.20
Purchase #2	$37.57	12.154%	$42.1363	$42.14	$42.15	$42.10
Purchase #3	$164.27	3.705%	$170.3562	$170.36	$170.35	$170.40
Purchase #4	$72.79	8.378%	$78.8883	$78.89	$78.90	$78.90
Purchase #5	$112.43	13.344%	$127.4327	$127.43	$127.45	$127.40
Purchase #6	$118.62	7.516%	$127.5355	$127.54	$127.55	$127.50
Purchase #7	$228.56	5.268%	$240.6005	$240.60	$240.60	$240.60
7 purchase totals =	$861.67		$931.1608	$931.17	$931.20	$931.10