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	$128.77	7.476%	$138.3968	$138.40	$138.40	$138.40
Purchase #2	$50.45	7.489%	$54.2282	$54.23	$54.25	$54.20
Purchase #3	$143.96	4.255%	$150.0855	$150.09	$150.10	$150.10
Purchase #4	$82.75	3.300%	$85.4808	$85.48	$85.50	$85.50
Purchase #5	$201.26	3.421%	$208.1451	$208.15	$208.15	$208.10
Purchase #6	$167.80	5.417%	$176.8897	$176.89	$176.90	$176.90
Purchase #7	$6.87	9.796%	$7.543	$7.54	$7.55	$7.50
7 purchase totals =	$781.86		$820.7691	$820.78	$820.85	$820.70