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	$56.52	9.390%	$61.8272	$61.83	$61.85	$61.80
Purchase #2	$63.31	5.706%	$66.9225	$66.92	$66.90	$66.90
Purchase #3	$122.46	12.417%	$137.6659	$137.67	$137.65	$137.70
Purchase #4	$199.27	11.714%	$222.6125	$222.61	$222.60	$222.60
Purchase #5	$172.83	6.581%	$184.2039	$184.20	$184.20	$184.20
Purchase #6	$27.42	13.871%	$31.2234	$31.22	$31.20	$31.20
Purchase #7	$134.50	4.815%	$140.9762	$140.98	$141.00	$141.00
7 purchase totals =	$776.31		$845.4316	$845.43	$845.40	$845.40