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	$80.52	12.232%	$90.3692	$90.37	$90.35	$90.40
Purchase #2	$58.68	12.691%	$66.1271	$66.13	$66.15	$66.10
Purchase #3	$128.32	12.236%	$144.0212	$144.02	$144.00	$144.00
Purchase #4	$212.28	7.702%	$228.6298	$228.63	$228.65	$228.60
Purchase #5	$157.83	13.630%	$179.3422	$179.34	$179.35	$179.30
Purchase #6	$174.30	7.801%	$187.8971	$187.90	$187.90	$187.90
Purchase #7	$109.46	3.706%	$113.5166	$113.52	$113.50	$113.50
7 purchase totals =	$921.39		$1,009.9032	$1,009.91	$1,009.90	$1,009.80