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	$124.46	5.804%	$131.6837	$131.68	$131.70	$131.70
Purchase #2	$240.34	12.106%	$269.4356	$269.44	$269.45	$269.40
Purchase #3	$40.51	7.694%	$43.6268	$43.63	$43.65	$43.60
Purchase #4	$114.48	10.270%	$126.2371	$126.24	$126.25	$126.20
Purchase #5	$124.89	13.209%	$141.3867	$141.39	$141.40	$141.40
Purchase #6	$29.49	9.400%	$32.2621	$32.26	$32.25	$32.30
Purchase #7	$106.55	5.398%	$112.3016	$112.30	$112.30	$112.30
7 purchase totals =	$780.72		$856.9336	$856.94	$857.00	$856.90