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	$231.27	9.735%	$253.7841	$253.78	$253.80	$253.80
Purchase #2	$236.67	13.371%	$268.3151	$268.32	$268.30	$268.30
Purchase #3	$49.30	9.342%	$53.9056	$53.91	$53.90	$53.90
Purchase #4	$45.35	4.757%	$47.5073	$47.51	$47.50	$47.50
Purchase #5	$21.79	4.495%	$22.7695	$22.77	$22.75	$22.80
Purchase #6	$152.42	12.393%	$171.3094	$171.31	$171.30	$171.30
Purchase #7	$7.38	3.555%	$7.6424	$7.64	$7.65	$7.60
7 purchase totals =	$744.18		$825.2334	$825.24	$825.20	$825.20