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	$199.47	13.152%	$225.7043	$225.70	$225.70	$225.70
Purchase #2	$10.30	8.417%	$11.167	$11.17	$11.15	$11.20
Purchase #3	$173.36	9.403%	$189.661	$189.66	$189.65	$189.70
Purchase #4	$134.48	12.155%	$150.826	$150.83	$150.85	$150.80
Purchase #5	$38.45	13.285%	$43.5581	$43.56	$43.55	$43.60
Purchase #6	$19.39	10.508%	$21.4275	$21.43	$21.45	$21.40
Purchase #7	$123.90	6.167%	$131.5409	$131.54	$131.55	$131.50
7 purchase totals =	$699.35		$773.8848	$773.89	$773.90	$773.90