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	$92.41	8.248%	$100.032	$100.03	$100.05	$100.00
Purchase #2	$116.85	12.756%	$131.7554	$131.76	$131.75	$131.80
Purchase #3	$27.61	3.662%	$28.6211	$28.62	$28.60	$28.60
Purchase #4	$33.89	7.824%	$36.5416	$36.54	$36.55	$36.50
Purchase #5	$82.53	8.653%	$89.6713	$89.67	$89.65	$89.70
Purchase #6	$175.82	13.725%	$199.9513	$199.95	$199.95	$200.00
Purchase #7	$179.42	4.386%	$187.2894	$187.29	$187.30	$187.30
7 purchase totals =	$708.53		$773.8621	$773.86	$773.85	$773.90