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	$26.29	8.244%	$28.4573	$28.46	$28.45	$28.50
Purchase #2	$247.45	13.345%	$280.4722	$280.47	$280.45	$280.50
Purchase #3	$76.69	13.358%	$86.9343	$86.93	$86.95	$86.90
Purchase #4	$150.56	11.840%	$168.3863	$168.39	$168.40	$168.40
Purchase #5	$94.96	8.838%	$103.3526	$103.35	$103.35	$103.40
Purchase #6	$56.93	13.425%	$64.5729	$64.57	$64.55	$64.60
Purchase #7	$188.48	11.728%	$210.5849	$210.58	$210.60	$210.60
7 purchase totals =	$841.36		$942.7605	$942.75	$942.75	$942.90