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	$50.87	3.746%	$52.7756	$52.78	$52.80	$52.80
Purchase #2	$245.79	12.484%	$276.4744	$276.47	$276.45	$276.50
Purchase #3	$130.29	5.363%	$137.2775	$137.28	$137.30	$137.30
Purchase #4	$170.56	4.722%	$178.6138	$178.61	$178.60	$178.60
Purchase #5	$139.59	4.326%	$145.6287	$145.63	$145.65	$145.60
Purchase #6	$178.78	4.247%	$186.3728	$186.37	$186.35	$186.40
Purchase #7	$124.38	5.429%	$131.1326	$131.13	$131.15	$131.10
7 purchase totals =	$1,040.26		$1,108.2754	$1,108.27	$1,108.30	$1,108.30