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	$103.41	3.116%	$106.6323	$106.63	$106.65	$106.60
Purchase #2	$250.34	12.138%	$280.7263	$280.73	$280.75	$280.70
Purchase #3	$43.37	13.780%	$49.3464	$49.35	$49.35	$49.30
Purchase #4	$172.90	7.319%	$185.5546	$185.55	$185.55	$185.60
Purchase #5	$173.61	13.202%	$196.53	$196.53	$196.55	$196.50
Purchase #6	$109.57	10.844%	$121.4518	$121.45	$121.45	$121.50
Purchase #7	$85.85	5.816%	$90.843	$90.84	$90.85	$90.80
7 purchase totals =	$939.05		$1,031.0844	$1,031.08	$1,031.15	$1,031.00