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	$241.27	6.223%	$256.2842	$256.28	$256.30	$256.30
Purchase #2	$248.86	3.200%	$256.8235	$256.82	$256.80	$256.80
Purchase #3	$201.27	6.547%	$214.4471	$214.45	$214.45	$214.40
Purchase #4	$101.76	11.415%	$113.3759	$113.38	$113.40	$113.40
Purchase #5	$92.67	8.543%	$100.5868	$100.59	$100.60	$100.60
Purchase #6	$225.65	3.608%	$233.7915	$233.79	$233.80	$233.80
Purchase #7	$197.88	9.410%	$216.5005	$216.50	$216.50	$216.50
7 purchase totals =	$1,309.36		$1,391.8095	$1,391.81	$1,391.85	$1,391.80