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	$249.86	4.789%	$261.8258	$261.83	$261.85	$261.80
Purchase #2	$120.86	10.487%	$133.5346	$133.53	$133.55	$133.50
Purchase #3	$242.42	13.412%	$274.9334	$274.93	$274.95	$274.90
Purchase #4	$196.38	10.757%	$217.5046	$217.50	$217.50	$217.50
Purchase #5	$113.83	8.164%	$123.1231	$123.12	$123.10	$123.10
Purchase #6	$6.55	10.289%	$7.2239	$7.22	$7.20	$7.20
Purchase #7	$239.26	12.735%	$269.7298	$269.73	$269.75	$269.70
7 purchase totals =	$1,169.16		$1,287.8752	$1,287.86	$1,287.90	$1,287.70