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	$37.82	5.316%	$39.8305	$39.83	$39.85	$39.80
Purchase #2	$190.31	5.565%	$200.9008	$200.90	$200.90	$200.90
Purchase #3	$33.32	8.434%	$36.1302	$36.13	$36.15	$36.10
Purchase #4	$124.57	4.480%	$130.1507	$130.15	$130.15	$130.20
Purchase #5	$68.81	10.786%	$76.2318	$76.23	$76.25	$76.20
Purchase #6	$118.71	9.664%	$130.1821	$130.18	$130.20	$130.20
Purchase #7	$46.95	10.666%	$51.9577	$51.96	$51.95	$52.00
7 purchase totals =	$620.49		$665.3838	$665.38	$665.45	$665.40