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	$152.26	11.577%	$169.8871	$169.89	$169.90	$169.90
Purchase #2	$167.79	9.337%	$183.4566	$183.46	$183.45	$183.50
Purchase #3	$26.80	13.712%	$30.4748	$30.47	$30.45	$30.50
Purchase #4	$86.86	4.513%	$90.78	$90.78	$90.80	$90.80
Purchase #5	$74.73	10.478%	$82.5602	$82.56	$82.55	$82.60
Purchase #6	$222.91	12.267%	$250.2544	$250.25	$250.25	$250.30
Purchase #7	$46.67	9.376%	$51.0458	$51.05	$51.05	$51.00
7 purchase totals =	$778.02		$858.4589	$858.46	$858.45	$858.60