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	$166.91	8.434%	$180.9872	$180.99	$181.00	$181.00
Purchase #2	$115.73	5.294%	$121.8567	$121.86	$121.85	$121.90
Purchase #3	$125.41	5.200%	$131.9313	$131.93	$131.95	$131.90
Purchase #4	$156.47	12.654%	$176.2697	$176.27	$176.25	$176.30
Purchase #5	$85.80	4.141%	$89.353	$89.35	$89.35	$89.40
Purchase #6	$78.63	13.638%	$89.3536	$89.35	$89.35	$89.40
Purchase #7	$177.97	6.809%	$190.088	$190.09	$190.10	$190.10
7 purchase totals =	$906.92		$979.8395	$979.84	$979.85	$980.00