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	$39.35	9.466%	$43.0749	$43.07	$43.05	$43.10
Purchase #2	$47.69	9.716%	$52.3236	$52.32	$52.30	$52.30
Purchase #3	$85.98	5.305%	$90.5412	$90.54	$90.55	$90.50
Purchase #4	$41.92	13.222%	$47.4627	$47.46	$47.45	$47.50
Purchase #5	$93.55	5.700%	$98.8824	$98.88	$98.90	$98.90
Purchase #6	$199.85	9.412%	$218.6599	$218.66	$218.65	$218.70
Purchase #7	$24.78	3.803%	$25.7224	$25.72	$25.70	$25.70
7 purchase totals =	$533.12		$576.6671	$576.65	$576.60	$576.70