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	$92.52	12.665%	$104.2377	$104.24	$104.25	$104.20
Purchase #2	$55.74	8.730%	$60.6061	$60.61	$60.60	$60.60
Purchase #3	$62.39	8.264%	$67.5459	$67.55	$67.55	$67.50
Purchase #4	$91.56	10.856%	$101.4998	$101.50	$101.50	$101.50
Purchase #5	$233.96	7.337%	$251.1256	$251.13	$251.15	$251.10
Purchase #6	$143.62	13.165%	$162.5276	$162.53	$162.55	$162.50
Purchase #7	$233.59	9.536%	$255.8651	$255.87	$255.85	$255.90
7 purchase totals =	$913.38		$1,003.4078	$1,003.43	$1,003.45	$1,003.30