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	$240.36	6.643%	$256.3271	$256.33	$256.35	$256.30
Purchase #2	$187.62	9.645%	$205.7159	$205.72	$205.70	$205.70
Purchase #3	$83.41	8.838%	$90.7818	$90.78	$90.80	$90.80
Purchase #4	$201.69	7.339%	$216.492	$216.49	$216.50	$216.50
Purchase #5	$199.40	6.138%	$211.6392	$211.64	$211.65	$211.60
Purchase #6	$72.93	7.493%	$78.3946	$78.39	$78.40	$78.40
Purchase #7	$45.47	3.616%	$47.1142	$47.11	$47.10	$47.10
7 purchase totals =	$1,030.88		$1,106.4648	$1,106.46	$1,106.50	$1,106.40