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	$179.97	9.331%	$196.763	$196.76	$196.75	$196.80
Purchase #2	$218.90	11.265%	$243.5591	$243.56	$243.55	$243.60
Purchase #3	$11.88	13.505%	$13.4844	$13.48	$13.50	$13.50
Purchase #4	$97.42	6.855%	$104.0981	$104.10	$104.10	$104.10
Purchase #5	$110.89	7.535%	$119.2456	$119.25	$119.25	$119.20
Purchase #6	$164.89	5.407%	$173.8056	$173.81	$173.80	$173.80
Purchase #7	$47.74	8.720%	$51.9029	$51.90	$51.90	$51.90
7 purchase totals =	$831.69		$902.8587	$902.86	$902.85	$902.90