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	$38.53	7.484%	$41.4136	$41.41	$41.40	$41.40
Purchase #2	$114.38	4.782%	$119.8497	$119.85	$119.85	$119.80
Purchase #3	$19.69	4.308%	$20.5382	$20.54	$20.55	$20.50
Purchase #4	$46.38	7.805%	$50	$50.00	$50.00	$50.00
Purchase #5	$113.75	12.782%	$128.2895	$128.29	$128.30	$128.30
Purchase #6	$73.89	13.493%	$83.86	$83.86	$83.85	$83.90
Purchase #7	$124.70	9.859%	$136.9942	$136.99	$137.00	$137.00
7 purchase totals =	$531.32		$580.9452	$580.94	$580.95	$580.90