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	$244.84	10.765%	$271.197	$271.20	$271.20	$271.20
Purchase #2	$235.82	3.395%	$243.8261	$243.83	$243.85	$243.80
Purchase #3	$185.69	5.601%	$196.0905	$196.09	$196.10	$196.10
Purchase #4	$190.44	10.156%	$209.7811	$209.78	$209.80	$209.80
Purchase #5	$227.57	10.272%	$250.946	$250.95	$250.95	$250.90
Purchase #6	$36.70	10.124%	$40.4155	$40.42	$40.40	$40.40
Purchase #7	$102.55	9.594%	$112.3886	$112.39	$112.40	$112.40
7 purchase totals =	$1,223.61		$1,324.6448	$1,324.66	$1,324.70	$1,324.60