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	$30.40	3.590%	$31.4914	$31.49	$31.50	$31.50
Purchase #2	$11.71	9.458%	$12.8175	$12.82	$12.80	$12.80
Purchase #3	$64.65	4.245%	$67.3944	$67.39	$67.40	$67.40
Purchase #4	$223.90	6.550%	$238.5655	$238.57	$238.55	$238.60
Purchase #5	$6.35	12.324%	$7.1326	$7.13	$7.15	$7.10
Purchase #6	$88.69	3.159%	$91.4917	$91.49	$91.50	$91.50
Purchase #7	$13.94	7.667%	$15.0088	$15.01	$15.00	$15.00
7 purchase totals =	$439.64		$463.9019	$463.90	$463.90	$463.90