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	$52.52	4.230%	$54.7416	$54.74	$54.75	$54.70
Purchase #2	$192.77	6.635%	$205.5603	$205.56	$205.55	$205.60
Purchase #3	$144.77	8.375%	$156.8945	$156.89	$156.90	$156.90
Purchase #4	$135.98	5.520%	$143.4861	$143.49	$143.50	$143.50
Purchase #5	$30.58	8.551%	$33.1949	$33.19	$33.20	$33.20
Purchase #6	$137.83	6.135%	$146.2859	$146.29	$146.30	$146.30
Purchase #7	$28.89	9.494%	$31.6328	$31.63	$31.65	$31.60
7 purchase totals =	$723.34		$771.7961	$771.79	$771.85	$771.80