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	$103.80	7.700%	$111.7926	$111.79	$111.80	$111.80
Purchase #2	$207.85	4.687%	$217.5919	$217.59	$217.60	$217.60
Purchase #3	$123.70	13.702%	$140.6494	$140.65	$140.65	$140.60
Purchase #4	$174.99	6.783%	$186.8596	$186.86	$186.85	$186.90
Purchase #5	$220.32	13.529%	$250.1271	$250.13	$250.15	$250.10
Purchase #6	$137.47	12.513%	$154.6716	$154.67	$154.65	$154.70
Purchase #7	$182.48	3.210%	$188.3376	$188.34	$188.35	$188.30
7 purchase totals =	$1,150.61		$1,250.0298	$1,250.03	$1,250.05	$1,250.00