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	$128.85	12.103%	$144.4447	$144.44	$144.45	$144.40
Purchase #2	$196.71	7.391%	$211.2488	$211.25	$211.25	$211.20
Purchase #3	$81.61	10.154%	$89.8967	$89.90	$89.90	$89.90
Purchase #4	$57.87	11.392%	$64.4626	$64.46	$64.45	$64.50
Purchase #5	$122.88	7.247%	$131.7851	$131.79	$131.80	$131.80
Purchase #6	$79.81	9.469%	$87.3672	$87.37	$87.35	$87.40
Purchase #7	$52.28	7.133%	$56.0091	$56.01	$56.00	$56.00
7 purchase totals =	$720.01		$785.2142	$785.22	$785.20	$785.20