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	$52.26	8.188%	$56.539	$56.54	$56.55	$56.50
Purchase #2	$36.63	7.388%	$39.3362	$39.34	$39.35	$39.30
Purchase #3	$206.52	7.739%	$222.5026	$222.50	$222.50	$222.50
Purchase #4	$12.93	9.210%	$14.1209	$14.12	$14.10	$14.10
Purchase #5	$240.36	4.577%	$251.3613	$251.36	$251.35	$251.40
Purchase #6	$29.78	12.475%	$33.4951	$33.50	$33.50	$33.50
Purchase #7	$199.50	11.563%	$222.5682	$222.57	$222.55	$222.60
7 purchase totals =	$777.98		$839.9233	$839.93	$839.90	$839.90