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	$202.88	13.622%	$230.5163	$230.52	$230.50	$230.50
Purchase #2	$36.88	4.684%	$38.6075	$38.61	$38.60	$38.60
Purchase #3	$160.85	9.310%	$175.8251	$175.83	$175.85	$175.80
Purchase #4	$121.49	8.349%	$131.6332	$131.63	$131.65	$131.60
Purchase #5	$212.95	11.588%	$237.6266	$237.63	$237.65	$237.60
Purchase #6	$145.83	9.414%	$159.5584	$159.56	$159.55	$159.60
Purchase #7	$28.90	9.309%	$31.5903	$31.59	$31.60	$31.60
7 purchase totals =	$909.78		$1,005.3574	$1,005.37	$1,005.40	$1,005.30