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	$84.75	13.746%	$96.3997	$96.40	$96.40	$96.40
Purchase #2	$154.98	12.771%	$174.7725	$174.77	$174.75	$174.80
Purchase #3	$132.50	5.299%	$139.5212	$139.52	$139.50	$139.50
Purchase #4	$247.61	9.801%	$271.8783	$271.88	$271.90	$271.90
Purchase #5	$69.52	13.548%	$78.9386	$78.94	$78.95	$78.90
Purchase #6	$40.81	5.206%	$42.9346	$42.93	$42.95	$42.90
Purchase #7	$119.57	5.238%	$125.8331	$125.83	$125.85	$125.80
7 purchase totals =	$849.74		$930.2780	$930.27	$930.30	$930.20