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	$151.46	13.228%	$171.4951	$171.50	$171.50	$171.50
Purchase #2	$173.37	9.331%	$189.5472	$189.55	$189.55	$189.50
Purchase #3	$128.33	13.775%	$146.0075	$146.01	$146.00	$146.00
Purchase #4	$184.46	6.411%	$196.2857	$196.29	$196.30	$196.30
Purchase #5	$124.38	12.289%	$139.6651	$139.67	$139.65	$139.70
Purchase #6	$60.85	13.240%	$68.9065	$68.91	$68.90	$68.90
Purchase #7	$161.89	8.768%	$176.0845	$176.08	$176.10	$176.10
7 purchase totals =	$984.74		$1,087.9916	$1,088.01	$1,088.00	$1,088.00