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	$25.45	7.341%	$27.3183	$27.32	$27.30	$27.30
Purchase #2	$100.63	13.193%	$113.9061	$113.91	$113.90	$113.90
Purchase #3	$154.93	13.365%	$175.6364	$175.64	$175.65	$175.60
Purchase #4	$144.51	5.372%	$152.2731	$152.27	$152.25	$152.30
Purchase #5	$90.53	11.474%	$100.9174	$100.92	$100.90	$100.90
Purchase #6	$94.76	7.572%	$101.9352	$101.94	$101.95	$101.90
Purchase #7	$112.64	11.564%	$125.6657	$125.67	$125.65	$125.70
7 purchase totals =	$723.45		$797.6522	$797.67	$797.60	$797.60