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	$248.37	4.378%	$259.2436	$259.24	$259.25	$259.20
Purchase #2	$110.84	5.128%	$116.5239	$116.52	$116.50	$116.50
Purchase #3	$105.77	3.494%	$109.4656	$109.47	$109.45	$109.50
Purchase #4	$46.25	5.347%	$48.723	$48.72	$48.70	$48.70
Purchase #5	$38.32	13.690%	$43.566	$43.57	$43.55	$43.60
Purchase #6	$109.34	5.193%	$115.018	$115.02	$115.00	$115.00
Purchase #7	$228.77	9.439%	$250.3636	$250.36	$250.35	$250.40
7 purchase totals =	$887.66		$942.9037	$942.90	$942.80	$942.90