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	$63.51	10.379%	$70.1017	$70.10	$70.10	$70.10
Purchase #2	$65.68	12.577%	$73.9406	$73.94	$73.95	$73.90
Purchase #3	$38.96	10.711%	$43.133	$43.13	$43.15	$43.10
Purchase #4	$30.61	5.858%	$32.4031	$32.40	$32.40	$32.40
Purchase #5	$137.72	12.578%	$155.0424	$155.04	$155.05	$155.00
Purchase #6	$114.50	11.820%	$128.0339	$128.03	$128.05	$128.00
Purchase #7	$83.91	12.680%	$94.5498	$94.55	$94.55	$94.50
7 purchase totals =	$534.89		$597.2045	$597.19	$597.25	$597.00