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	$101.83	3.865%	$105.7657	$105.77	$105.75	$105.80
Purchase #2	$197.73	11.118%	$219.7136	$219.71	$219.70	$219.70
Purchase #3	$43.32	8.210%	$46.8766	$46.88	$46.90	$46.90
Purchase #4	$192.39	12.301%	$216.0559	$216.06	$216.05	$216.10
Purchase #5	$117.55	8.177%	$127.1621	$127.16	$127.15	$127.20
Purchase #6	$161.85	7.610%	$174.1668	$174.17	$174.15	$174.20
Purchase #7	$7.78	3.720%	$8.0694	$8.07	$8.05	$8.10
7 purchase totals =	$822.45		$897.8101	$897.82	$897.75	$898.00