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	$99.44	5.669%	$105.0773	$105.08	$105.10	$105.10
Purchase #2	$248.64	10.177%	$273.9441	$273.94	$273.95	$273.90
Purchase #3	$149.82	7.521%	$161.088	$161.09	$161.10	$161.10
Purchase #4	$112.55	9.592%	$123.3458	$123.35	$123.35	$123.30
Purchase #5	$171.46	4.741%	$179.5889	$179.59	$179.60	$179.60
Purchase #6	$45.59	4.295%	$47.5481	$47.55	$47.55	$47.50
Purchase #7	$147.49	3.213%	$152.2289	$152.23	$152.25	$152.20
7 purchase totals =	$974.99		$1,042.8211	$1,042.83	$1,042.90	$1,042.70