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	$13.71	11.169%	$15.2413	$15.24	$15.25	$15.20
Purchase #2	$124.43	5.746%	$131.5797	$131.58	$131.60	$131.60
Purchase #3	$98.27	4.391%	$102.585	$102.59	$102.60	$102.60
Purchase #4	$119.51	7.577%	$128.5653	$128.57	$128.55	$128.60
Purchase #5	$91.33	9.240%	$99.7689	$99.77	$99.75	$99.80
Purchase #6	$105.49	7.354%	$113.2477	$113.25	$113.25	$113.20
Purchase #7	$49.25	3.647%	$51.0461	$51.05	$51.05	$51.00
7 purchase totals =	$601.99		$642.0340	$642.05	$642.05	$642.00