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	$209.35	13.168%	$236.9172	$236.92	$236.90	$236.90
Purchase #2	$98.87	4.812%	$103.6276	$103.63	$103.65	$103.60
Purchase #3	$190.72	12.301%	$214.1805	$214.18	$214.20	$214.20
Purchase #4	$179.38	9.260%	$195.9906	$195.99	$196.00	$196.00
Purchase #5	$98.63	10.583%	$109.068	$109.07	$109.05	$109.10
Purchase #6	$126.89	8.519%	$137.6998	$137.70	$137.70	$137.70
Purchase #7	$37.44	13.172%	$42.3716	$42.37	$42.35	$42.40
7 purchase totals =	$941.28		$1,039.8553	$1,039.86	$1,039.85	$1,039.90