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	$76.60	11.170%	$85.1562	$85.16	$85.15	$85.20
Purchase #2	$122.85	12.255%	$137.9053	$137.91	$137.90	$137.90
Purchase #3	$173.69	6.665%	$185.2664	$185.27	$185.25	$185.30
Purchase #4	$206.32	3.794%	$214.1478	$214.15	$214.15	$214.10
Purchase #5	$128.86	11.322%	$143.4495	$143.45	$143.45	$143.40
Purchase #6	$110.45	4.202%	$115.0911	$115.09	$115.10	$115.10
Purchase #7	$126.82	10.689%	$140.3758	$140.38	$140.40	$140.40
7 purchase totals =	$945.59		$1,021.3921	$1,021.41	$1,021.40	$1,021.40