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	$80.39	6.258%	$85.4208	$85.42	$85.40	$85.40
Purchase #2	$162.96	6.473%	$173.5084	$173.51	$173.50	$173.50
Purchase #3	$221.75	4.424%	$231.5602	$231.56	$231.55	$231.60
Purchase #4	$85.32	9.508%	$93.4322	$93.43	$93.45	$93.40
Purchase #5	$66.46	8.438%	$72.0679	$72.07	$72.05	$72.10
Purchase #6	$187.95	12.179%	$210.8404	$210.84	$210.85	$210.80
Purchase #7	$132.81	8.281%	$143.808	$143.81	$143.80	$143.80
7 purchase totals =	$937.64		$1,010.6379	$1,010.64	$1,010.60	$1,010.60