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	$43.83	12.635%	$49.3679	$49.37	$49.35	$49.40
Purchase #2	$174.35	7.264%	$187.0148	$187.01	$187.00	$187.00
Purchase #3	$108.33	4.251%	$112.9351	$112.94	$112.95	$112.90
Purchase #4	$167.27	9.689%	$183.4768	$183.48	$183.50	$183.50
Purchase #5	$50.82	4.449%	$53.081	$53.08	$53.10	$53.10
Purchase #6	$72.76	13.334%	$82.4618	$82.46	$82.45	$82.50
Purchase #7	$244.32	11.185%	$271.6472	$271.65	$271.65	$271.60
7 purchase totals =	$861.68		$939.9846	$939.99	$940.00	$940.00