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	$84.97	3.348%	$87.8148	$87.81	$87.80	$87.80
Purchase #2	$139.71	7.551%	$150.2595	$150.26	$150.25	$150.30
Purchase #3	$130.42	13.259%	$147.7124	$147.71	$147.70	$147.70
Purchase #4	$122.34	4.580%	$127.9432	$127.94	$127.95	$127.90
Purchase #5	$249.50	12.580%	$280.8871	$280.89	$280.90	$280.90
Purchase #6	$74.37	11.346%	$82.808	$82.81	$82.80	$82.80
Purchase #7	$237.83	11.762%	$265.8036	$265.80	$265.80	$265.80
7 purchase totals =	$1,039.14		$1,143.2286	$1,143.22	$1,143.20	$1,143.20