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	$115.99	10.456%	$128.1179	$128.12	$128.10	$128.10
Purchase #2	$214.42	3.590%	$222.1177	$222.12	$222.10	$222.10
Purchase #3	$178.46	4.125%	$185.8215	$185.82	$185.80	$185.80
Purchase #4	$102.49	6.855%	$109.5157	$109.52	$109.50	$109.50
Purchase #5	$113.72	4.827%	$119.2093	$119.21	$119.20	$119.20
Purchase #6	$55.43	10.366%	$61.1759	$61.18	$61.20	$61.20
Purchase #7	$42.46	6.526%	$45.2309	$45.23	$45.25	$45.20
7 purchase totals =	$822.97		$871.1889	$871.20	$871.15	$871.10