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	$71.47	12.694%	$80.5424	$80.54	$80.55	$80.50
Purchase #2	$64.47	11.760%	$72.0517	$72.05	$72.05	$72.10
Purchase #3	$68.99	13.106%	$78.0318	$78.03	$78.05	$78.00
Purchase #4	$236.66	11.777%	$264.5314	$264.53	$264.55	$264.50
Purchase #5	$171.94	8.579%	$186.6907	$186.69	$186.70	$186.70
Purchase #6	$54.83	11.533%	$61.1535	$61.15	$61.15	$61.20
Purchase #7	$83.91	9.759%	$92.0988	$92.10	$92.10	$92.10
7 purchase totals =	$752.27		$835.1003	$835.09	$835.15	$835.10