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	$140.87	10.582%	$155.7769	$155.78	$155.80	$155.80
Purchase #2	$151.76	13.224%	$171.8287	$171.83	$171.85	$171.80
Purchase #3	$167.59	10.800%	$185.6897	$185.69	$185.70	$185.70
Purchase #4	$167.73	8.589%	$182.1363	$182.14	$182.15	$182.10
Purchase #5	$106.82	3.705%	$110.7777	$110.78	$110.80	$110.80
Purchase #6	$44.93	5.723%	$47.5013	$47.50	$47.50	$47.50
Purchase #7	$18.67	8.474%	$20.2521	$20.25	$20.25	$20.30
7 purchase totals =	$798.37		$873.9627	$873.97	$874.05	$874.00