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	$246.81	12.465%	$277.5749	$277.57	$277.55	$277.60
Purchase #2	$249.71	9.257%	$272.8257	$272.83	$272.85	$272.80
Purchase #3	$220.69	12.568%	$248.4263	$248.43	$248.45	$248.40
Purchase #4	$132.80	3.103%	$136.9208	$136.92	$136.90	$136.90
Purchase #5	$148.93	13.422%	$168.9194	$168.92	$168.90	$168.90
Purchase #6	$6.67	12.487%	$7.5029	$7.50	$7.50	$7.50
Purchase #7	$94.72	6.522%	$100.8976	$100.90	$100.90	$100.90
7 purchase totals =	$1,100.33		$1,213.0676	$1,213.07	$1,213.05	$1,213.00