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	$11.56	4.699%	$12.1032	$12.10	$12.10	$12.10
Purchase #2	$61.40	8.621%	$66.6933	$66.69	$66.70	$66.70
Purchase #3	$213.89	4.478%	$223.468	$223.47	$223.45	$223.50
Purchase #4	$123.87	3.789%	$128.5634	$128.56	$128.55	$128.60
Purchase #5	$22.62	6.203%	$24.0231	$24.02	$24.00	$24.00
Purchase #6	$97.90	7.828%	$105.5636	$105.56	$105.55	$105.60
Purchase #7	$216.58	9.216%	$236.54	$236.54	$236.55	$236.50
7 purchase totals =	$747.82		$796.9546	$796.94	$796.90	$797.00