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	$108.68	9.820%	$119.3524	$119.35	$119.35	$119.40
Purchase #2	$84.32	4.705%	$88.2873	$88.29	$88.30	$88.30
Purchase #3	$56.52	3.562%	$58.5332	$58.53	$58.55	$58.50
Purchase #4	$132.28	13.824%	$150.5664	$150.57	$150.55	$150.60
Purchase #5	$79.85	7.596%	$85.9154	$85.92	$85.90	$85.90
Purchase #6	$86.46	13.611%	$98.2281	$98.23	$98.25	$98.20
Purchase #7	$63.93	4.191%	$66.6093	$66.61	$66.60	$66.60
7 purchase totals =	$612.04		$667.4921	$667.50	$667.50	$667.50