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	$36.90	3.601%	$38.2288	$38.23	$38.25	$38.20
Purchase #2	$18.82	6.290%	$20.0038	$20.00	$20.00	$20.00
Purchase #3	$176.85	4.350%	$184.543	$184.54	$184.55	$184.50
Purchase #4	$77.47	7.172%	$83.0261	$83.03	$83.05	$83.00
Purchase #5	$18.66	4.352%	$19.4721	$19.47	$19.45	$19.50
Purchase #6	$151.72	4.807%	$159.0132	$159.01	$159.00	$159.00
Purchase #7	$156.75	3.429%	$162.125	$162.13	$162.15	$162.10
7 purchase totals =	$637.17		$666.4120	$666.41	$666.45	$666.30