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	$247.41	13.521%	$280.8623	$280.86	$280.85	$280.90
Purchase #2	$243.68	12.587%	$274.352	$274.35	$274.35	$274.40
Purchase #3	$121.62	5.305%	$128.0719	$128.07	$128.05	$128.10
Purchase #4	$79.72	11.744%	$89.0823	$89.08	$89.10	$89.10
Purchase #5	$194.72	12.570%	$219.1963	$219.20	$219.20	$219.20
Purchase #6	$72.33	13.605%	$82.1705	$82.17	$82.15	$82.20
Purchase #7	$36.74	4.359%	$38.3415	$38.34	$38.35	$38.30
7 purchase totals =	$996.22		$1,112.0768	$1,112.07	$1,112.05	$1,112.20