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	$41.32	10.611%	$45.7045	$45.70	$45.70	$45.70
Purchase #2	$91.35	9.435%	$99.9689	$99.97	$99.95	$100.00
Purchase #3	$119.94	9.678%	$131.5478	$131.55	$131.55	$131.50
Purchase #4	$132.53	4.770%	$138.8517	$138.85	$138.85	$138.90
Purchase #5	$137.66	11.456%	$153.4303	$153.43	$153.45	$153.40
Purchase #6	$236.96	3.602%	$245.4953	$245.50	$245.50	$245.50
Purchase #7	$85.74	4.305%	$89.4311	$89.43	$89.45	$89.40
7 purchase totals =	$845.50		$904.4296	$904.43	$904.45	$904.40