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	$240.86	4.149%	$250.8533	$250.85	$250.85	$250.90
Purchase #2	$135.64	6.573%	$144.5556	$144.56	$144.55	$144.60
Purchase #3	$241.98	12.769%	$272.8784	$272.88	$272.90	$272.90
Purchase #4	$216.87	6.665%	$231.3244	$231.32	$231.30	$231.30
Purchase #5	$62.31	13.824%	$70.9237	$70.92	$70.90	$70.90
Purchase #6	$140.72	11.326%	$156.6579	$156.66	$156.65	$156.70
Purchase #7	$49.53	9.743%	$54.3557	$54.36	$54.35	$54.40
7 purchase totals =	$1,087.91		$1,181.5490	$1,181.55	$1,181.50	$1,181.70