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	$135.53	10.692%	$150.0209	$150.02	$150.00	$150.00
Purchase #2	$205.38	11.204%	$228.3908	$228.39	$228.40	$228.40
Purchase #3	$129.88	11.759%	$145.1526	$145.15	$145.15	$145.20
Purchase #4	$40.43	7.769%	$43.571	$43.57	$43.55	$43.60
Purchase #5	$134.99	9.806%	$148.2271	$148.23	$148.25	$148.20
Purchase #6	$203.92	11.456%	$227.2811	$227.28	$227.30	$227.30
Purchase #7	$79.94	11.804%	$89.3761	$89.38	$89.40	$89.40
7 purchase totals =	$930.07		$1,032.0196	$1,032.02	$1,032.05	$1,032.10