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	$104.93	3.311%	$108.4042	$108.40	$108.40	$108.40
Purchase #2	$36.73	5.168%	$38.6282	$38.63	$38.65	$38.60
Purchase #3	$181.91	4.686%	$190.4343	$190.43	$190.45	$190.40
Purchase #4	$109.38	13.143%	$123.7558	$123.76	$123.75	$123.80
Purchase #5	$38.33	9.595%	$42.0078	$42.01	$42.00	$42.00
Purchase #6	$92.48	6.318%	$98.3229	$98.32	$98.30	$98.30
Purchase #7	$13.28	4.141%	$13.8299	$13.83	$13.85	$13.80
7 purchase totals =	$577.04		$615.3831	$615.38	$615.40	$615.30