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	$97.53	12.337%	$109.5623	$109.56	$109.55	$109.60
Purchase #2	$155.89	12.510%	$175.3918	$175.39	$175.40	$175.40
Purchase #3	$98.71	3.357%	$102.0237	$102.02	$102.00	$102.00
Purchase #4	$175.67	9.858%	$192.9875	$192.99	$193.00	$193.00
Purchase #5	$95.88	10.491%	$105.9388	$105.94	$105.95	$105.90
Purchase #6	$126.94	12.158%	$142.3734	$142.37	$142.35	$142.40
Purchase #7	$114.46	11.645%	$127.7889	$127.79	$127.80	$127.80
7 purchase totals =	$865.08		$956.0664	$956.06	$956.05	$956.10