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	$51.85	6.786%	$55.3685	$55.37	$55.35	$55.40
Purchase #2	$238.84	12.162%	$267.8877	$267.89	$267.90	$267.90
Purchase #3	$95.63	9.192%	$104.4203	$104.42	$104.40	$104.40
Purchase #4	$227.37	5.873%	$240.7234	$240.72	$240.70	$240.70
Purchase #5	$213.57	8.446%	$231.6081	$231.61	$231.60	$231.60
Purchase #6	$14.27	7.145%	$15.2896	$15.29	$15.30	$15.30
Purchase #7	$157.76	6.382%	$167.8282	$167.83	$167.85	$167.80
7 purchase totals =	$999.29		$1,083.1258	$1,083.13	$1,083.10	$1,083.10