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	$239.80	4.713%	$251.1018	$251.10	$251.10	$251.10
Purchase #2	$72.63	8.252%	$78.6234	$78.62	$78.60	$78.60
Purchase #3	$101.82	4.694%	$106.5994	$106.60	$106.60	$106.60
Purchase #4	$14.77	7.726%	$15.9111	$15.91	$15.90	$15.90
Purchase #5	$205.37	9.620%	$225.1266	$225.13	$225.15	$225.10
Purchase #6	$84.66	11.689%	$94.5559	$94.56	$94.55	$94.60
Purchase #7	$27.60	3.578%	$28.5875	$28.59	$28.60	$28.60
7 purchase totals =	$746.65		$800.5057	$800.51	$800.50	$800.50