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	$40.89	11.840%	$45.7314	$45.73	$45.75	$45.70
Purchase #2	$156.50	13.699%	$177.9389	$177.94	$177.95	$177.90
Purchase #3	$202.84	5.211%	$213.41	$213.41	$213.40	$213.40
Purchase #4	$140.93	13.187%	$159.5144	$159.51	$159.50	$159.50
Purchase #5	$63.29	6.123%	$67.1652	$67.17	$67.15	$67.20
Purchase #6	$56.37	6.214%	$59.8728	$59.87	$59.85	$59.90
Purchase #7	$81.32	5.283%	$85.6161	$85.62	$85.60	$85.60
7 purchase totals =	$742.14		$809.2488	$809.25	$809.20	$809.20