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	$111.50	12.222%	$125.1275	$125.13	$125.15	$125.10
Purchase #2	$250.60	4.757%	$262.521	$262.52	$262.50	$262.50
Purchase #3	$40.61	9.518%	$44.4753	$44.48	$44.50	$44.50
Purchase #4	$104.37	3.723%	$108.2557	$108.26	$108.25	$108.30
Purchase #5	$162.54	10.159%	$179.0524	$179.05	$179.05	$179.10
Purchase #6	$85.36	4.482%	$89.1858	$89.19	$89.20	$89.20
Purchase #7	$173.80	3.184%	$179.3338	$179.33	$179.35	$179.30
7 purchase totals =	$928.78		$987.9515	$987.96	$988.00	$988.00