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	$235.57	8.397%	$255.3508	$255.35	$255.35	$255.40
Purchase #2	$249.47	7.402%	$267.9358	$267.94	$267.95	$267.90
Purchase #3	$170.41	10.143%	$187.6947	$187.69	$187.70	$187.70
Purchase #4	$250.44	11.458%	$279.1354	$279.14	$279.15	$279.10
Purchase #5	$131.94	11.166%	$146.6724	$146.67	$146.65	$146.70
Purchase #6	$45.70	3.158%	$47.1432	$47.14	$47.15	$47.10
Purchase #7	$38.90	12.849%	$43.8983	$43.90	$43.90	$43.90
7 purchase totals =	$1,122.43		$1,227.8306	$1,227.83	$1,227.85	$1,227.80