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	$244.93	13.447%	$277.8657	$277.87	$277.85	$277.90
Purchase #2	$108.67	6.751%	$116.0063	$116.01	$116.00	$116.00
Purchase #3	$229.34	13.829%	$261.0554	$261.06	$261.05	$261.10
Purchase #4	$81.60	9.727%	$89.5372	$89.54	$89.55	$89.50
Purchase #5	$138.25	3.331%	$142.8551	$142.86	$142.85	$142.90
Purchase #6	$94.69	7.780%	$102.0569	$102.06	$102.05	$102.10
Purchase #7	$87.27	13.830%	$99.3394	$99.34	$99.35	$99.30
7 purchase totals =	$984.75		$1,088.7160	$1,088.74	$1,088.70	$1,088.80