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	$249.32	10.109%	$274.5238	$274.52	$274.50	$274.50
Purchase #2	$54.35	9.676%	$59.6089	$59.61	$59.60	$59.60
Purchase #3	$152.71	4.648%	$159.808	$159.81	$159.80	$159.80
Purchase #4	$56.66	11.565%	$63.2127	$63.21	$63.20	$63.20
Purchase #5	$209.31	8.647%	$227.409	$227.41	$227.40	$227.40
Purchase #6	$39.61	3.162%	$40.8625	$40.86	$40.85	$40.90
Purchase #7	$102.60	7.665%	$110.4643	$110.46	$110.45	$110.50
7 purchase totals =	$864.56		$935.8892	$935.88	$935.80	$935.90