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	$179.92	3.867%	$186.8775	$186.88	$186.90	$186.90
Purchase #2	$67.63	12.646%	$76.1825	$76.18	$76.20	$76.20
Purchase #3	$177.72	7.672%	$191.3547	$191.35	$191.35	$191.40
Purchase #4	$54.72	3.765%	$56.7802	$56.78	$56.80	$56.80
Purchase #5	$11.69	3.408%	$12.0884	$12.09	$12.10	$12.10
Purchase #6	$52.94	13.209%	$59.9328	$59.93	$59.95	$59.90
Purchase #7	$100.94	13.731%	$114.8001	$114.80	$114.80	$114.80
7 purchase totals =	$645.56		$698.0162	$698.01	$698.10	$698.10