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	$102.73	9.529%	$112.5191	$112.52	$112.50	$112.50
Purchase #2	$83.74	12.424%	$94.1439	$94.14	$94.15	$94.10
Purchase #3	$197.27	13.370%	$223.645	$223.65	$223.65	$223.60
Purchase #4	$111.57	13.242%	$126.3441	$126.34	$126.35	$126.30
Purchase #5	$10.86	4.709%	$11.3714	$11.37	$11.35	$11.40
Purchase #6	$198.72	12.665%	$223.8879	$223.89	$223.90	$223.90
Purchase #7	$78.95	3.208%	$81.4827	$81.48	$81.50	$81.50
7 purchase totals =	$783.84		$873.3941	$873.39	$873.40	$873.30