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	$35.65	13.564%	$40.4856	$40.49	$40.50	$40.50
Purchase #2	$57.76	13.218%	$65.3947	$65.39	$65.40	$65.40
Purchase #3	$227.54	4.586%	$237.975	$237.98	$238.00	$238.00
Purchase #4	$192.96	8.242%	$208.8638	$208.86	$208.85	$208.90
Purchase #5	$95.28	11.417%	$106.1581	$106.16	$106.15	$106.20
Purchase #6	$204.35	9.393%	$223.5446	$223.54	$223.55	$223.50
Purchase #7	$49.73	10.680%	$55.0412	$55.04	$55.05	$55.00
7 purchase totals =	$863.27		$937.4630	$937.46	$937.50	$937.50