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	$20.50	6.798%	$21.8936	$21.89	$21.90	$21.90
Purchase #2	$36.86	10.308%	$40.6595	$40.66	$40.65	$40.70
Purchase #3	$103.78	9.256%	$113.3859	$113.39	$113.40	$113.40
Purchase #4	$136.85	3.441%	$141.559	$141.56	$141.55	$141.60
Purchase #5	$207.30	3.843%	$215.2665	$215.27	$215.25	$215.30
Purchase #6	$214.37	3.341%	$221.5321	$221.53	$221.55	$221.50
Purchase #7	$42.41	10.565%	$46.8906	$46.89	$46.90	$46.90
7 purchase totals =	$762.07		$801.1872	$801.19	$801.20	$801.30