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	$57.40	4.774%	$60.1403	$60.14	$60.15	$60.10
Purchase #2	$27.61	6.104%	$29.2953	$29.30	$29.30	$29.30
Purchase #3	$85.89	6.238%	$91.2478	$91.25	$91.25	$91.20
Purchase #4	$66.35	9.320%	$72.5338	$72.53	$72.55	$72.50
Purchase #5	$175.65	5.797%	$185.8324	$185.83	$185.85	$185.80
Purchase #6	$140.29	9.205%	$153.2037	$153.20	$153.20	$153.20
Purchase #7	$203.32	7.451%	$218.4694	$218.47	$218.45	$218.50
7 purchase totals =	$756.51		$810.7227	$810.72	$810.75	$810.60