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	$135.52	6.779%	$144.7069	$144.71	$144.70	$144.70
Purchase #2	$20.48	9.370%	$22.399	$22.40	$22.40	$22.40
Purchase #3	$192.89	4.578%	$201.7205	$201.72	$201.70	$201.70
Purchase #4	$133.66	3.105%	$137.8101	$137.81	$137.80	$137.80
Purchase #5	$195.37	10.266%	$215.4267	$215.43	$215.45	$215.40
Purchase #6	$38.89	12.677%	$43.8201	$43.82	$43.80	$43.80
Purchase #7	$78.30	5.270%	$82.4264	$82.43	$82.45	$82.40
7 purchase totals =	$795.11		$848.3097	$848.32	$848.30	$848.20