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	$30.91	8.850%	$33.6455	$33.65	$33.65	$33.60
Purchase #2	$138.56	12.239%	$155.5184	$155.52	$155.50	$155.50
Purchase #3	$130.35	7.301%	$139.8669	$139.87	$139.85	$139.90
Purchase #4	$116.82	5.621%	$123.3865	$123.39	$123.40	$123.40
Purchase #5	$47.62	7.484%	$51.1839	$51.18	$51.20	$51.20
Purchase #6	$137.63	13.483%	$156.1867	$156.19	$156.20	$156.20
Purchase #7	$140.71	4.488%	$147.0251	$147.03	$147.05	$147.00
7 purchase totals =	$742.60		$806.8130	$806.83	$806.85	$806.80