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	$85.26	5.643%	$90.0712	$90.07	$90.05	$90.10
Purchase #2	$51.29	6.536%	$54.6423	$54.64	$54.65	$54.60
Purchase #3	$131.93	7.577%	$141.9263	$141.93	$141.95	$141.90
Purchase #4	$30.78	7.314%	$33.0312	$33.03	$33.05	$33.00
Purchase #5	$237.55	4.691%	$248.6935	$248.69	$248.70	$248.70
Purchase #6	$100.81	4.516%	$105.3626	$105.36	$105.35	$105.40
Purchase #7	$185.62	12.625%	$209.0545	$209.05	$209.05	$209.10
7 purchase totals =	$823.24		$882.7816	$882.77	$882.80	$882.80