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	$83.43	7.388%	$89.5938	$89.59	$89.60	$89.60
Purchase #2	$17.25	6.392%	$18.3526	$18.35	$18.35	$18.40
Purchase #3	$6.87	8.778%	$7.473	$7.47	$7.45	$7.50
Purchase #4	$42.37	6.102%	$44.9554	$44.96	$44.95	$45.00
Purchase #5	$133.88	7.830%	$144.3628	$144.36	$144.35	$144.40
Purchase #6	$188.54	6.360%	$200.5311	$200.53	$200.55	$200.50
Purchase #7	$56.27	10.496%	$62.1761	$62.18	$62.20	$62.20
7 purchase totals =	$528.61		$567.4448	$567.44	$567.45	$567.60