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	$249.55	7.544%	$268.3761	$268.38	$268.40	$268.40
Purchase #2	$35.34	7.291%	$37.9166	$37.92	$37.90	$37.90
Purchase #3	$68.91	13.749%	$78.3844	$78.38	$78.40	$78.40
Purchase #4	$122.75	12.825%	$138.4927	$138.49	$138.50	$138.50
Purchase #5	$233.64	10.736%	$258.7236	$258.72	$258.70	$258.70
Purchase #6	$156.94	9.206%	$171.3879	$171.39	$171.40	$171.40
Purchase #7	$129.91	5.531%	$137.0953	$137.10	$137.10	$137.10
7 purchase totals =	$997.04		$1,090.3766	$1,090.38	$1,090.40	$1,090.40