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	$74.72	8.178%	$80.8306	$80.83	$80.85	$80.80
Purchase #2	$215.32	8.768%	$234.1993	$234.20	$234.20	$234.20
Purchase #3	$94.38	4.381%	$98.5148	$98.51	$98.50	$98.50
Purchase #4	$215.93	9.651%	$236.7694	$236.77	$236.75	$236.80
Purchase #5	$56.37	7.810%	$60.7725	$60.77	$60.75	$60.80
Purchase #6	$179.44	6.124%	$190.4289	$190.43	$190.45	$190.40
Purchase #7	$89.62	12.524%	$100.844	$100.84	$100.85	$100.80
7 purchase totals =	$925.78		$1,002.3595	$1,002.35	$1,002.35	$1,002.30