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	$22.61	8.210%	$24.4663	$24.47	$24.45	$24.50
Purchase #2	$88.76	3.187%	$91.5888	$91.59	$91.60	$91.60
Purchase #3	$225.37	10.847%	$249.8159	$249.82	$249.80	$249.80
Purchase #4	$155.73	5.559%	$164.387	$164.39	$164.40	$164.40
Purchase #5	$61.59	9.498%	$67.4398	$67.44	$67.45	$67.40
Purchase #6	$31.34	10.360%	$34.5868	$34.59	$34.60	$34.60
Purchase #7	$238.76	8.765%	$259.6873	$259.69	$259.70	$259.70
7 purchase totals =	$824.16		$891.9719	$891.99	$892.00	$892.00