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	$90.68	4.569%	$94.8232	$94.82	$94.80	$94.80
Purchase #2	$81.47	7.425%	$87.5191	$87.52	$87.50	$87.50
Purchase #3	$94.70	5.787%	$100.1803	$100.18	$100.20	$100.20
Purchase #4	$176.93	6.824%	$189.0037	$189.00	$189.00	$189.00
Purchase #5	$38.69	10.861%	$42.8921	$42.89	$42.90	$42.90
Purchase #6	$37.63	12.571%	$42.3605	$42.36	$42.35	$42.40
Purchase #7	$103.28	11.578%	$115.2378	$115.24	$115.25	$115.20
7 purchase totals =	$623.38		$672.0167	$672.01	$672.00	$672.00