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	$38.30	12.389%	$43.045	$43.05	$43.05	$43.00
Purchase #2	$68.54	7.139%	$73.4331	$73.43	$73.45	$73.40
Purchase #3	$11.45	12.612%	$12.8941	$12.89	$12.90	$12.90
Purchase #4	$34.39	7.514%	$36.9741	$36.97	$36.95	$37.00
Purchase #5	$190.84	3.188%	$196.924	$196.92	$196.90	$196.90
Purchase #6	$82.63	9.282%	$90.2997	$90.30	$90.30	$90.30
Purchase #7	$121.41	13.280%	$137.5332	$137.53	$137.55	$137.50
7 purchase totals =	$547.56		$591.1032	$591.09	$591.10	$591.00