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	$123.45	11.194%	$137.269	$137.27	$137.25	$137.30
Purchase #2	$204.90	13.267%	$232.0841	$232.08	$232.10	$232.10
Purchase #3	$116.86	12.362%	$131.3062	$131.31	$131.30	$131.30
Purchase #4	$109.81	12.785%	$123.8492	$123.85	$123.85	$123.80
Purchase #5	$9.89	8.578%	$10.7384	$10.74	$10.75	$10.70
Purchase #6	$166.84	11.767%	$186.4721	$186.47	$186.45	$186.50
Purchase #7	$95.25	3.631%	$98.7085	$98.71	$98.70	$98.70
7 purchase totals =	$827.00		$920.4275	$920.43	$920.40	$920.40