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	$240.72	13.857%	$274.0766	$274.08	$274.10	$274.10
Purchase #2	$38.28	6.201%	$40.6537	$40.65	$40.65	$40.70
Purchase #3	$224.49	5.530%	$236.9043	$236.90	$236.90	$236.90
Purchase #4	$31.79	6.712%	$33.9237	$33.92	$33.90	$33.90
Purchase #5	$61.98	3.706%	$64.277	$64.28	$64.30	$64.30
Purchase #6	$130.40	9.229%	$142.4346	$142.43	$142.45	$142.40
Purchase #7	$175.50	8.714%	$190.7931	$190.79	$190.80	$190.80
7 purchase totals =	$903.16		$983.0630	$983.05	$983.10	$983.10