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	$127.46	13.235%	$144.3293	$144.33	$144.35	$144.30
Purchase #2	$156.33	13.239%	$177.0265	$177.03	$177.05	$177.00
Purchase #3	$103.88	7.349%	$111.5141	$111.51	$111.50	$111.50
Purchase #4	$52.71	8.167%	$57.0148	$57.01	$57.00	$57.00
Purchase #5	$119.84	12.102%	$134.343	$134.34	$134.35	$134.30
Purchase #6	$88.59	12.123%	$99.3298	$99.33	$99.35	$99.30
Purchase #7	$145.61	7.141%	$156.008	$156.01	$156.00	$156.00
7 purchase totals =	$794.42		$879.5655	$879.56	$879.60	$879.40