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	$165.40	7.702%	$178.1391	$178.14	$178.15	$178.10
Purchase #2	$41.28	4.481%	$43.1298	$43.13	$43.15	$43.10
Purchase #3	$119.85	11.120%	$133.1773	$133.18	$133.20	$133.20
Purchase #4	$127.90	9.495%	$140.0441	$140.04	$140.05	$140.00
Purchase #5	$59.64	9.254%	$65.1591	$65.16	$65.15	$65.20
Purchase #6	$124.80	12.849%	$140.8356	$140.84	$140.85	$140.80
Purchase #7	$95.26	5.326%	$100.3335	$100.33	$100.35	$100.30
7 purchase totals =	$734.13		$800.8185	$800.82	$800.90	$800.70