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	$229.92	12.609%	$258.9106	$258.91	$258.90	$258.90
Purchase #2	$101.60	4.799%	$106.4758	$106.48	$106.50	$106.50
Purchase #3	$40.90	6.310%	$43.4808	$43.48	$43.50	$43.50
Purchase #4	$186.69	5.542%	$197.0364	$197.04	$197.05	$197.00
Purchase #5	$132.99	7.782%	$143.3393	$143.34	$143.35	$143.30
Purchase #6	$186.90	5.748%	$197.643	$197.64	$197.65	$197.60
Purchase #7	$69.40	4.646%	$72.6243	$72.62	$72.60	$72.60
7 purchase totals =	$948.40		$1,019.5102	$1,019.51	$1,019.55	$1,019.40