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	$109.62	12.642%	$123.4782	$123.48	$123.50	$123.50
Purchase #2	$139.42	4.233%	$145.3216	$145.32	$145.30	$145.30
Purchase #3	$141.53	8.745%	$153.9068	$153.91	$153.90	$153.90
Purchase #4	$238.70	9.540%	$261.472	$261.47	$261.45	$261.50
Purchase #5	$161.73	12.275%	$181.5824	$181.58	$181.60	$181.60
Purchase #6	$10.57	11.404%	$11.7754	$11.78	$11.80	$11.80
Purchase #7	$52.43	12.281%	$58.8689	$58.87	$58.85	$58.90
7 purchase totals =	$854.00		$936.4053	$936.41	$936.40	$936.50