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	$243.98	10.693%	$270.0688	$270.07	$270.05	$270.10
Purchase #2	$139.31	10.269%	$153.6157	$153.62	$153.60	$153.60
Purchase #3	$174.77	9.369%	$191.1442	$191.14	$191.15	$191.10
Purchase #4	$151.45	3.554%	$156.8325	$156.83	$156.85	$156.80
Purchase #5	$29.98	5.191%	$31.5363	$31.54	$31.55	$31.50
Purchase #6	$43.95	8.331%	$47.6115	$47.61	$47.60	$47.60
Purchase #7	$158.32	8.862%	$172.3503	$172.35	$172.35	$172.40
7 purchase totals =	$941.76		$1,023.1593	$1,023.16	$1,023.15	$1,023.10