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	$92.25	4.559%	$96.4557	$96.46	$96.45	$96.50
Purchase #2	$61.61	7.755%	$66.3879	$66.39	$66.40	$66.40
Purchase #3	$227.67	12.443%	$255.999	$256.00	$256.00	$256.00
Purchase #4	$170.37	6.429%	$181.3231	$181.32	$181.30	$181.30
Purchase #5	$134.26	11.814%	$150.1215	$150.12	$150.10	$150.10
Purchase #6	$100.96	8.858%	$109.903	$109.90	$109.90	$109.90
Purchase #7	$71.95	9.499%	$78.7845	$78.78	$78.80	$78.80
7 purchase totals =	$859.07		$938.9747	$938.97	$938.95	$939.00