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	$39.83	12.289%	$44.7247	$44.72	$44.70	$44.70
Purchase #2	$63.81	7.329%	$68.4866	$68.49	$68.50	$68.50
Purchase #3	$18.51	12.457%	$20.8158	$20.82	$20.80	$20.80
Purchase #4	$152.86	13.722%	$173.8354	$173.84	$173.85	$173.80
Purchase #5	$83.48	11.321%	$92.9308	$92.93	$92.95	$92.90
Purchase #6	$117.40	12.292%	$131.8308	$131.83	$131.85	$131.80
Purchase #7	$61.40	10.494%	$67.8433	$67.84	$67.85	$67.80
7 purchase totals =	$537.29		$600.4674	$600.47	$600.50	$600.30