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	$246.83	7.268%	$264.7696	$264.77	$264.75	$264.80
Purchase #2	$6.96	4.758%	$7.2912	$7.29	$7.30	$7.30
Purchase #3	$16.46	12.418%	$18.504	$18.50	$18.50	$18.50
Purchase #4	$128.44	9.202%	$140.259	$140.26	$140.25	$140.30
Purchase #5	$64.89	12.243%	$72.8345	$72.83	$72.85	$72.80
Purchase #6	$235.91	11.135%	$262.1786	$262.18	$262.20	$262.20
Purchase #7	$66.40	9.631%	$72.795	$72.80	$72.80	$72.80
7 purchase totals =	$765.89		$838.6319	$838.63	$838.65	$838.70