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	$129.93	13.314%	$147.2289	$147.23	$147.25	$147.20
Purchase #2	$130.26	9.762%	$142.976	$142.98	$143.00	$143.00
Purchase #3	$198.78	8.610%	$215.895	$215.90	$215.90	$215.90
Purchase #4	$6.29	13.220%	$7.1215	$7.12	$7.10	$7.10
Purchase #5	$209.94	10.302%	$231.568	$231.57	$231.55	$231.60
Purchase #6	$152.29	4.365%	$158.9375	$158.94	$158.95	$158.90
Purchase #7	$164.40	12.789%	$185.4251	$185.43	$185.45	$185.40
7 purchase totals =	$991.89		$1,089.1520	$1,089.17	$1,089.20	$1,089.10