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	$125.88	10.457%	$139.0433	$139.04	$139.05	$139.00
Purchase #2	$210.41	5.792%	$222.5969	$222.60	$222.60	$222.60
Purchase #3	$111.91	4.458%	$116.8989	$116.90	$116.90	$116.90
Purchase #4	$112.41	13.794%	$127.9158	$127.92	$127.90	$127.90
Purchase #5	$225.79	3.216%	$233.0514	$233.05	$233.05	$233.10
Purchase #6	$84.41	13.545%	$95.8433	$95.84	$95.85	$95.80
Purchase #7	$47.40	9.753%	$52.0229	$52.02	$52.00	$52.00
7 purchase totals =	$918.21		$987.3725	$987.37	$987.35	$987.30